Last modified: Jun 17, 2024

Dynamic expressions

Overview of dynamic expressions defined in JSON

On this page:

⚠️ Dynamic behaviour is an area under active development. This functionality is currently available as a beta feature in Altinn Studio and offers limited configuration options. The UI only allows to build expressions with one level of nesting, meaning an unlimited number of un-nested expressions can be combined using either the OR or AND operator. However, the tool allows to edit more complicated expressions by freestyle writing. Currently the tool is also limited to connecting expression to boolean component fields. See Expressions in Altinn Studio on how to use Altinn Studio to configure an expression.

Introduction

Dynamic expressions enable the definition of simple dynamic behavior in an Altinn 3 app, such as defining whether a form field should be shown or hidden, whether the field should be required or read-only.

These expressions are available in all Altinn 3 apps that use frontend version 3.54.0 or later. By using this version or the latest major version, you can use dynamic expressions for several use cases.

Starting from version 7.2.0 of the nuget packages the expressions are also supported in the backend. This means that the server will be able to evaluate the expressions and remove data upon submission that is potentially stored in the data model /*9+and is associated with fields/components that are later hidden. Note that this only applies to data in the data model that is associated with hidden components - data in the data model that is not associated with components (and is thus implicitly hidden from the user) will not be automatically removed.

It also makes it possible to omit submitting data that is otherwise associated with required fields - if these required fields are hidden in the form using dynamic expressions. This also applies when submitting directly from the API.

Note: Note that automatic removal of hidden data must currently be manually activated (opt-in) by adding the following line to App/appsettings.json after upgrading the nuget packages to 7.2.0 or later:

      "AppSettings": {
        "OpenIdWellKnownEndpoint": "http://localhost:5101/authentication/api/v1/openid/",
        "RuntimeCookieName": "AltinnStudioRuntime",
        "RegisterEventsWithEventsComponent": false,
        "RemoveHiddenData": true
      },
    
      "AppSettings": {
        "OpenIdWellKnownEndpoint": "http://localhost:5101/authentication/api/v1/openid/",
        "RuntimeCookieName": "AltinnStudioRuntime",
        "RegisterEventsWithEventsComponent": false,
        "RemoveHiddenDataPreview": true
      },
    

    Structure and syntax

    Structure and syntax:

    The expressions are built up as a kind of mini-programming language, where everything is defined in JSON. The expressions themselves are always a list (array) of values, where the first value in each list is always a function name. The rest of the values are sent as input/arguments to the function.

    ["equals", "foo", "bar"]
    

    In the example above, the strings “foo” and “bar” are compared. They are different, so the result of this expression is a boolean value; false.

    This function, equals, expects to receive two strings as input/arguments. It is also possible to give it another expression as the second argument. If you do this, the expression will be interpreted so that the innermost functions are executed first, and the outermost ones are executed last

    ["equals", ["component", "firstName"], "John"]
    

    In this example, the innermost expression/function call [“component”, “firstName”] is executed first. If the value of the “firstName” component is equal to the string “John”, the function returns the boolean value “true”.

    If you then use this expression for the hidden property of a component, the component will be hidden if you enter “John” in the “firstName” component elsewhere in the application:

    {
      "id": "lastName",
      "type": "Input",
      ...
      "hidden": ["equals", ["component", "firstName"], "John"]
    }
    ```json
    
    There are no limitations on how large/deep the expressions can be. As an exercise, see if you can read what this 
    expression does, and what possible values it can return:
    ```json
    [
      "if",
      ["greaterThanEq", ["component", "age"], 16],
      [
        "if",
        ["lessThan", ["component", "age"], 62],
        "Please consider applying for our open position!",
        "else",
        ["concat", "At ", ["component", "age"], ", you are eligible for retirement"]
      ],
      "else",
      ["concat", "At ", ["component", "age"], ", you should stay in (pre)school"]
    ]
    

    The expression checks the value of a hypothetical component with ID “age”. If the person is 16 years or older, for example 45 years old, the text “Please consider applying for our open position!” is returned if the age is less than 62. Otherwise, the text “At 45, you are eligible for retirement” is returned. If the person is younger than 16, the text “At 5, you should stay in (pre)school” is returned, assuming the age is 5.

    Please consider applying for our open position!

    For a person who is 62 years old, the text returned is:

    At 62, your are eligible for retirement

    And for a person who is 15 years old (or younger, such as a 4-year-old), the text returned is:

    At 4, you should stay in (pre)school


    Use Cases

    Dynamic expressions are currently available for use in these properties, as defined in layout files.

    ComponentsPropertyExpected ValueFrontendBackend
    Pages/layoutshiddenBoolean
    AllhiddenBoolean
    Form componentsrequiredBoolean
    Form componentsreadOnlyBoolean
    Repeating groupshiddenRowBoolean
    Repeating groupsedit.addButtonBoolean
    Repeating groupsedit.saveButtonBoolean
    Repeating groupsedit.deleteButtonBoolean
    Repeating groupsedit.alertOnDeleteBoolean
    Repeating groupsedit.saveAndNextButtonBoolean
    RadioButtons, Checkboxes, Dropdownsource.labelString
    RadioButtons, Checkboxes, Dropdownsource.descriptionString
    RadioButtons, Checkboxes, Dropdownsource.helpTextString
    AlltextResourceBindings.[*] *String

    * = The values that can be overridden with textResourceBindings vary from component to component, but will work wherever used. For repeating groups, you can find more information here

    Here we change the text of the edit button in a repeating group based on whether IsPrefill is set to true in a given address in the data model. If IsPrefill is true for an address, the row displaying that address will have an edit button with the text "View". If IsPrefill is false, the button text will be "Edit" for that specific row.

    It is worth to mention that if a lookup on IsPrefill returns null (not found), the result is converted to false when used in an if. Read more about this in the sections on if and data types

    {
      "id": "repeatingAddressGroup",
      "type": "Group",
      "children": ["field-id-one", "field-id-two"],
      "dataModelBindings": {
        "group": "Citizen.FormerAdresses"
      },
      "maxCount": 10,
      "textResourceBindings": {
        "edit_button_open": [
          "if",
          ["dataModel", "Citizen.FormerAdresses.IsPrefill"],
          "View",
          "else",
          "Edit"
        ]
      }
    }
    

    Testing, feilsøking og utvikling av uttrykk

    Testing, Debugging, and Developing Expressions

    When writing an expression, it’s useful to have an idea of what the result will be and whether the expression is valid. Invalid expressions will give a warning in the JavaScript console in the browser when the page loads, so it’s a good idea to have this console open when developing an application and testing expressions locally.

    It’s also possible to test the execution of an expression directly in the developer tools. This is done by pressing Ctrl + Shift + K (or Cmd + Shift + K on Mac) and navigating to the expression tab. Expressions may behave differently depending on the component they are evaluated near. Therefore, you can also select a component to be used as context when evaluating the expression in the developer tools.

    Note: This describes some implementation details in app-frontend-react and is only relevant when testing an expression in the developer tools that depends on a known position in a repeating group. This may change in the future, and such changes will not affect expressions defined in an application. The context is retrieved from where the expression is defined in the layout file.

    Imagine a repeating group for people with two fields: name and age. Given the following expression:

    ["component", "age"]

    What will the age be? It may vary depending on which group evaluates the expression. If there are two groups/rows, both the name and age components will exist twice. These will have IDs name-0 and age-0 (for the first row) and name-1 and age-1 (for the second row).

    Imagine the following data is filled in a repeating group:

    NameComponent IDAgeComponent ID
    Pername-024age-0
    Kariname-136age-1
    Olaname-218age-2

    Given the following expression:

    ["component", "age"]
    

    And with these assumptions:

    1. No context has been given (or the expression is placed on a component that is not near an age component)
    2. The expression is evaluated in the context of name-0
    3. The expression is evaluated in the context of name-1

    What will the result be in the different examples? Here are the answers:

    1. This will find the “first and best” age component and thus find age-0. It therefore returns 24, Per’s age.
    2. Here, we try to search in the context of the name component on the first row, and again we find 24, Per’s age.
    3. In the last example, we have specified the second row in the repeating group by evaluating in the context of name-1. Here we find the closest age component age-1, which is 36, Kari’s age.

    Functions

    These functions are available for use in expressions:

    Function NameParametersReturn ValueFrontendBackend
    equalsString, StringBoolean
    notEqualsString, StringBoolean
    notBooleanBoolean
    greaterThanNumber, NumberBoolean
    greaterThanEqNumber, NumberBoolean
    lessThanNumber, NumberBoolean
    lessThanEqNumber, NumberBoolean
    concatNone or multiple stringsString
    andOne or more boolean valuesBoolean
    orOne or more boolean valuesBoolean
    ifSee detailed descriptionSee detailed description
    containsString, StringBoolean
    notContainsString, StringBoolean
    commaContainsString, StringBoolean
    startsWithString, StringBoolean
    endsWithString, StringBoolean
    lowerCaseStringString
    upperCaseStringString
    stringLengthStringNumber
    textStringString
    languageNoneString
    displayValueStringString
    roundNumber, optional NumberString
    instanceContextStringString
    frontendSettingsStringString
    dataModelStringString
    componentStringString
    formatDateString, optional StringString
    linkToPageString, StringString
    linkToComponentString, StringString

    Detailed descriptions and examples

    These two functions compare two strings to check if they are equal (equals) or not equal (notEquals). If you send in values other than strings, the values are converted and compared as strings (read more about conversion here).

    Examples:

    {
      "id": "lastName",
      "type": "Input",
      ...
      "hidden": ["equals",
        ["dataModel", "My.Model.FirstName"],
        "Ola"
      ],
      "readOnly": ["notEquals",
        ["frontendSettings", "FormIsEditable"],
        true
      ]
    }
    

    notEquals is essentially the same as, and a shortcut to, ["not", ["equals", ...]].

    See also tips and tricks under String or less string comparison?

    This function takes in a boolean value or something that can be converted to a boolean value and returns the opposite boolean value. True becomes false, false becomes true.

    The function can be useful if you want to invert an expression. Instead of thinking about writing an expression that hides a component given certain conditions, you can wrap the expression in not and write the expression based on what is needed to show the component:

    {
      "id": "lastName",
      "type": "Input",
      "hidden": [
        "not",
        ["or", ["dataModel", "ShowLastName"], ["frontendSettings", "ShowAllFields"]]
      ]
    }
    

    These 4 functions expect two input numbers and compare whether the first is compared with the second. That is, for the function greaterThan, the expression is true if the first number is greater than the second.

    FunctionDescriptionSymbol
    greaterThanIs the first number greater than the second number?>
    greaterThanEqIs the first number greater than or equal to the second number?
    lessThanIs the first number less than the second number?<
    lessThanEqIs the first number less than or equal to the second number?

    If any of the arguments to these functions are null, the result will be false (regardless of whether it is the first or second argument).

    Example checking if age is over (or equal to) 18:

    ["greaterThanEq", ["component", "alder"], 18]
    

    This function takes 0 or more strings as arguments and returns a string where all the strings in the arguments are concatenated. If the function is called without any arguments, it returns an empty string.

    Note that the function doesn’t automatically add spaces or commas when concatenating strings. To provide a more readable result, it’s recommended to add dashes where necessary:

    ["concat", "Congratulations on your ", ["component", "age"], "th birthday!"]
    

    The expression above gives the text Congratulations on your 18th-birthday! if the value in the age component was 18.

    In the concat-function, null-values are interpreted as empty strings. Boolean values are output as the strings “true” and “false”.

    The functions and and or expect 1 or more boolean values and produce a result based on whether all or at least one of the values were true (true).

    FunctionDescription
    andAre all the arguments true? (true)
    orIs at least one of the arguments true? (true)

    Providing null values will interpret them as false (false). Examples of usage can be found under String or smaller string comparison?

    The if function can be used to branch an expression so that the return value is controlled by the result of another boolean expression. The function can be called in two different ways: with 2 or 4 arguments:

    ArgumentAlternative 1Alternative 2
    First argumentBooleanBoolean
    Second argumentAny typeAny type
    Third argumentThe string "else"
    Fourth argumentAny type

    In alternative 1, the return value of the function will be the value given as the second argument if the first argument is true (true). If not, it returns the value null.

    In alternative 2, the return value of the function will be the value given as the second argument if the first argument is true (true). If not, it returns the value given in the fourth argument. You must always provide the string "else" as the third argument if you want to call the function with 4 arguments. The third argument is only there to make the expression more readable and serves no other function.

    If you want more conditions and possible return values, you can nest multiple if calls inside the second or fourth argument:

    [
      "if",
      ["greaterThan", ["component", "birthYear"], 1945],
      "You were born after the World Wars",
      "else",
      [
        "if",
        ["greaterThanEq", ["component", "birthYear"], 1939],
        "You were born during World War II",
        "else",
        "You were born before World War II"
      ]
    ]
    

    The function language returns the user’s selected language code.

    Example:

    {
       "id": "lastName",
       "type": "Input",
       ...
       "readOnly": ["equal", ["language"], "en"],
    }
    

    If the current language is unknown, nb will be returned, which is the default language for Altinn 3 apps. Therefore, you can be confident that this function always returns a valid language.

    Note: This function is not yet available in backend code. Consequently, it will generate an error message if used in places where expressions run on the backend, and if the functionality to automatically delete hidden data (RemoveHiddenDataPreview) has been enabled.

    The startsWith function checks if the string provided as the first argument starts with the string given in the second argument. Similarly, the endsWith function checks if the first string ends with the second string.

    ["startsWith", ["dataModel", "My.Model.FirstName"], "Jo"]
    
    ["endsWith", ["dataModel", "My.Model.FirstName"], "hn"]
    

    Some important details about these functions:

    • All functions start and end with an empty string, so startsWith and endsWith will always return true if using an expression like ["startsWith", "...", ""]. This is crucial to consider when using the value of a component or a lookup in the data model as the second argument.
    • No strings start or end with a null value. If an expression like this is used:
      [
        "startsWith",
        ["dataModel", "My.Model.FullName"],
        ["dataModel", "My.Model.FirstName"]
      ]
      

    the result will always be false as long as the first name is not provided. However, as mentioned earlier, if the first name is set to an empty string (for example, if the user has erased their first name), the expression will return true if a full name is set. To avoid some of this behavior, you can use the if function together with equals to check if something is set to an empty string.

    • ["startsWith", null, null] always returns false.

    The function stringLength returns the length of a string (in number of letters/characters), including spaces.

    Example:

    ["stringLength", ["dataModel", "My.Model.FirstName"]]
    

    If the string is null, stringLength will return 0.

    These two functions check whether string A includes or does not include string B. Both contains and notContains are case-sensitive. This means that the string “Hei” does not include “hei”. If you want to compare regardless of case, you can use the functions lowerCase or upperCase along with contains or notContains.

    Example:

    {
       "id": "lastName",
       "type": "Input",
       ...
       "hidden": [
          "contains",
          ["dataModel", "My.Model.FirstName"],
          "J"
       ],
       "readOnly": [
          "notContains",
          ["dataModel", "My.Model.FirstName"],
          "D"
       ]
    }
    

    If you want to check for values in a comma-separated list, you can use the function commaContains.

    The function commaContains takes two arguments. The first argument is a comma-separated string, and the second argument is the string you want to check if it’s among the comma-separated values in the first argument.

    Example:

    {
       "id": "addName",
       "type": "Input",
       ...
       "readOnly": ["commaContains", ["dataModel", "My.Model.Names"], "Ola"]
    }
    

    Note that any spaces before/after commas or before/after the first value are ignored. This function is particularly useful in cases where you use a component that stores multiple values in a comma-separated string, such as Checkboxes and MultipleSelect.

    The functions lowerCase and upperCase take a string as input and return a new string where all characters are converted to lowercase or uppercase, respectively.

    ["lowerCase", ["dataModel", "My.Model.LastName"]]
    

    These functions provide a simple way to convert between lowercase and uppercase letters within a string. One use case could be combining one of these functions with other comparison functions so that the comparisons are done regardless of whether uppercase or lowercase letters were used in the input value.

    ["equals", ["upperCase", ["dataModel", "My.Model.LastName"]], "SMITH"]
    

    The function round rounds a number to an integer or, optionally, to a decimal number with a configurable number of decimal places.

    Example of rounding to 2 decimal places:

    ["round", "122.99843", "2"]
    

    Example of rounding to the nearest integer:

    ["round", "3.4999"]
    

    The return value from this function is a string, allowing it to be used for display purposes (note that the decimal separator is always a period). Even though the return value is a string, it can also be used further in expressions that expect numeric input.

    The function text takes a key as an argument and uses this key to retrieve the corresponding text from a text resource. The function returns the value associated with the specified key.

    Example:

    ["text", "min-nøkkel-id"]
    

    Note: Remember to manually test with text keys that contain variables. It’s not guaranteed that these will work as expected.

    Note: This function is not yet available in backend code. Therefore, it will generate an error message if used in places where expressions run on the backend, and if the functionality to automatically delete hidden data (RemoveHiddenDataPreview) has been enabled.

    The function displayValue looks up a component and returns a formatted text string representing the value in the data model. This differs from the component function, which returns the raw value in the data model. This function is best suited for displaying a component’s value to the user and less for further logic based on the returned value. This is particularly relevant for Input fields with number formatting, date fields, radio buttons (and other components with code lists), etc.

    Example:

    ["displayValue", "component-id"]
    

    Note: This function is not yet available in backend code. Therefore, it will generate an error message if used in places where expressions run on the backend, and if the functionality to automatically delete hidden data (RemoveHiddenDataPreview) has been enabled.

    This function allows retrieving information about the current instance. The following keys can be used as the first argument:

    KeyValueExample Value
    instanceIdCurrent instance ID512345/48c31ffc-dcdd-416d-8bc7-194bec3b7bf0
    instanceOwnerPartyIdCurrent actor ID512345
    instanceOwnerPartyTypeType of actor owning instance"org", "person", "selfIdentified", or "unknown"
    appIdID of the active apporg/app-name

    All these lookups will return a value of null if working in a stateless context. Using keys other than those listed above will result in an error message. This behavior is unique among lookup functions to ensure that information not (yet) exposed via a key here is not attempted to be retrieved from the instance. Provide feedback if you wish to retrieve instance data not available in this function.

    The lookup is performed in the same data source available for language/texts.

    This post allows retrieving information from a data source that can be controlled differently for each runtime environment.

    The lookup is performed within the same data source available for language/texts, and the setup is detailed there.

    Note: The data source is named applicationSettings when used in language/texts, but the values must always be stored under the key FrontEndSettings in appsettings.{environment}.json. For this reason, the function has been named frontendSettings here to indicate that lookups cannot be performed in the rest of appsettings.{environment}.json.

    This lookup function enables retrieving values directly from the current data model. The first and only argument must point to a location in the data model and uses the same dot-separated format as used in dataModelBindings. When used within repeating groups, there’s no need to use placeholders for indexes within the group - the expression automatically finds the relative position within the context of a repeating group.

    Please note that lookups only function against data types already supported in the expressions. If one looks up an object or a list/array in the data model using the dataModel function, the result will always be null. This functionality may change, as there are plans to support objects and lists in the expressions in the future.

    Example of lookup within a repeating group:

    [
       {
          "id": "employees",
          "type": "Group",
          "textResourceBindings": {
             "title": "Employees in the company"
          },
          "maxCount": 99999,
          "children": ["employee-name", "employee-age"],
          "dataModelBindings": {
             "group": "Employees"
          }
       },
       {
          "id": "employee-name",
          "type": "Input",
          "textResourceBindings": {
             "title": "Full Name"
          },
          "dataModelBindings": {
             "simpleBinding": "Employees.Name"
          },
          "hidden": ["lessThan",
            ["dataModel", "Employees.Age"],
            18]
       },
       {
          "id": "employee-age",
          "type": "Input",
          "textResourceBindings": {
             "title": "Age"
          },
          "dataModelBindings": {
             "simpleBinding": "Employees.Age"
          },
          "hidden": ["equals",
            ["dataModel", "Employees[0].Name"],
            "Ola Nordmann"]
       }
    ]
    

    The following observations can be made:

    1. The first lookup (to control hidden on the component employee-name) is governed by the age of each employee. If the employee is under 18 years old, employee-name is hidden. Note that the same path in the data model is used as simpleBinding on employee-age.

    2. The second lookup (to control hidden on the component employee-age) uses [0] in the data model lookup. This also works, but the behavior might be unexpected; here, all age components are hidden if the name of the first employee is Ola Nordmann.

    Direct lookups on a component are, in many ways, similar to lookups in the data model using dataModel. An expression that looks up the value of a component will search for the component and return the value stored in its simpleBinding in the data model. Currently, no other values are supported besides the one stored against simpleBinding (if other values are desired, one must directly access dataModel).

    However, a lookup on a component will return null if the component whose value is being looked up is hidden (even if the component otherwise has associated data in the data model). This, to some extent, allows controlling the display of a component based on whether another component is visible or not. If the component is found on a completely different (yet hidden) page, the lookup also yields null, even if the data model has a value associated with the component.

    Similar to dataModel, lookups on a component ID will attempt to find the component in the vicinity of the expression within the context of repeating groups. It will first search for the component in the current row before looking up through the page structure.

    The formatDate function takes a date as its first argument, and a format as its second argument. The date argument is a string, while the format argument is an optional string that supports some tokens in Unicode Tokens.

    These are the tokens we support:

    UnitTokenResult
    EraG..GGGBC, AD
    EraGGGGBefore Christ, Anno Domini
    EraGGGGGB, A
    Yeary44, 1, 1900, 2017
    Yearyy44, 01, 00, 17
    Yearyyy044, 001, 1900, 2017
    Yearyyyy0044, 0001, 1900, 2017
    Extended yearu-43, 0, 1, 1900, 2017
    Extended yearuu-43, 01, 1900, 2017
    Extended yearuuu-043, 001, 1900, 2017
    Extended yearuuuu-0043, 0001, 1900, 2017
    MonthM1, 2,…, 12
    MonthMM01, 02,…, 12
    MonthMMMJan, Feb, …, Dec
    MonthMMMMJanuary, February, …, December
    Day of monthd1, 2, …, 31
    Day of monthdd01, 02, …, 31
    Day of weekE..EEEMon, Tue, Wed, …, Sun
    Day of weekEEEEMonday, Tuesday, Wednesday, …, Sunday
    Day of weekEEEEEM, T, W, …, S
    AM/PMaa.m., p.m.
    Hour [1-12]h1, 2, …, 11, 12
    Hour [1-12]hh01, 02, …, 11, 12
    Hour [0-23]H1, 2, …, 22, 23
    Hour [0-23]HH01, 02, …, 22, 23
    Minutem1, 2, …, 59
    Minutemm01, 02, …, 59
    Seconds1, 2, …, 59
    Secondss01, 02, …, 59
    Fractional secondS0, 1, …, 9
    Fractional secondSS00, 01, …, 99
    Fractional secondSSS000, 001, …, 999

    If the format argument is not provided, the function will use the format MM/dd/yy as default. Example:

    ["formatDate", "2023-10-30T14:54:00.000Z", "HH:mm"]
    

    Would result in 14:54

    The linkToPage function can be used to create links that can be used inside text in a form. It is meant to create links that point to a specific page of the form. Clicking this link will navigate directly to the specified page.

    The function takes 2 arguments. The first argument is the link text which will be visible for the user. The second argument is the id of the page the link should point to.

    ["linkToPage", "Specify your name", "page1"]
    

    Would result in <a href="#/instance/<party-id>/<instance-id>/<TaskId>/page1">Specify your name</a> When clicked, this link will take the user to the specified page.

    The linkToComponent function can be used to create links that can be used inside text in a form. It is meant to create links that point to a specific component of the form. Clicking this link will navigate directly to the component, giving it focus.

    The function takes 2 arguments. The first argument is the link text which will be visible for the user. The second argument is the id of the component the link should point to.

    ["linkToComponent", "Specify your name", "inputMyName"]
    

    Would result in <a href="#/instance/<party-id>/<instance-id>/<TaskId>/<PageId>?focusNodeId=inputMyName">Specify your name</a> When clicked, this link will take the user to the page the component is on and focus on the specified component.

    Data Types

    Expressions in the functions expect that the arguments sent in have a specific type. If an argument sent in has a different type than expected, the value is attempted to be converted to the correct type. For instance, the function equals expects two strings, but if you send in the boolean value true as either argument, it works fine too because the boolean value true is converted to the string "true".

    ["equals", true, "true"]
    

    The expression above works and yields true as a result (because true and "true" are compared as the same value by converting true to "true" before comparison). This also allows calling a function that returns one datatype and, for example, comparing it with a completely different datatype. Read more about which datatypes can be converted to what below.

    All functions expecting a specific datatype as an argument will also function if you send in null. However, in some cases, using a null value may result in an error message – for instance, attempting to look up in the data model with ["dataModel", null]. In the concat function, however, a null value is interpreted as an empty string.

    Strings

    Strings contain arbitrary text and are a broad datatype that can be converted from numbers and boolean values.

    Some strings can also be converted to other datatypes:

    String ValueCan SubstituteExamples
    Integers with or without negative signsNumber3, -8, 71254
    Decimal numbers with or without negative signsNumber3.14, -33.0, 123.123
    true or false with lowercase or uppercaseBooleantrue, True, FALSE
    null with lowercase or uppercaseNullnull, Null, NULL

    All other strings not listed in the table above will result in an error if attempted to be converted to other types.

    Numbers

    Numeric values refer to positive and negative integers and decimal numbers. Some strings are also automatically converted to a numeric value, as shown in the table for strings above. For a string to be successfully converted to a number, the string must meet the following criteria:

    • The string contains only a number, with no other text before or after it.
    • A negative sign (-) can be used, but a positive sign (+) is not supported.
    • Decimal numbers must be represented with a period, not a comma.
    • Thousands separators or other number formatting are not supported.

    All other strings will result in an error if attempted to be converted to a number. Attempting to convert a boolean value to a number will also result in an error.

    Functions expecting a numeric input can also receive null. See more about its impact in the description of each function.

    Boolean Values

    Boolean values include true (true) and false (false). When calling a function expecting a boolean value, certain other types can also be passed, which are converted to a boolean value:

    • The numbers 1 and 0 function as true and false, respectively.
    • The strings "1" and "0" function similarly to the numbers (and become true and false, respectively).
    • The strings "true" and "false" are also converted to a boolean value.
    • The value null functions like false.

    All other values will result in an error if passed to a function expecting a boolean value. Note that these rules differ slightly from the rules for strings. Thus, there is a difference between values that can be interpreted as a boolean value for a function expecting a boolean argument and values that are equal to a boolean value. The function equals compares values as strings, so the number 1 and the string "1" will be considered equal, but it will not recognize 1 and true as equal values.

    It might appear that the following expressions are similar:

    1. "hidden": ["dataModel", "hideName"]
    2. "hidden": ["equals", ["dataModel", "hideName"], true]
    3. "hidden": ["if", ["dataModel", "hideName"], true, "else", false]

    If the value (here obtained from the lookup ["dataModel", "hideName"]) is true or "true", the component will be hidden. However, if the value is 1 or "1", the component will only be hidden with expressions in options 1 and 3. This is because the result in the hidden expression is converted to a boolean value, and if expects a boolean value as the first argument. However, equals compares the values as strings, and "1" is not equal to "true".

    Also, see tips and tricks under String or not a string comparison?

    Null

    Most places where a string, number, or boolean value is expected should also handle a null value. Null values indicate that a specific value is missing, and there is a difference between a null value, an empty string, and the number 0.

    If you perform a lookup in a function like dataModel, and the value you are searching for is not found/set, usually null will be the result.

    Tips and Tricks

    Show/Hide Entire Pages

    Expressions can be used to show/hide entire pages. In the example below, the entire page will be hidden if a component (on one of the other pages) has the value no or is not set.

    {
       "$schema": "https://altinncdn.no/toolkits/altinn-app-frontend/4/schemas/json/layout/layout.schema.v1.json",
       "data": {
          "hidden": ["or",
             ["equals", ["component", "hasComplaints"], "no"],
             ["equals", ["component", "hasComplaints"], null]
          ],
          "layout": [
             ...
          ]
       }
    }
    

    If the page you are on is hidden, the application will automatically move to the next available page in the page order. If all the next pages are hidden, the first possible page in the order will be displayed instead.

    String or smaller String Comparison?

    The way expressions are evaluated might seem strict (for example, 0 and null are considered different values when compared with equals). This is a design choice made in Altinn for two reasons:

    1. Strict rules are clear rules. The expressions are more likely to provide an error message if something is not as expected rather than leaving you wondering why things turned out the way they did.
    2. If the expressions treat many different values as equal, it takes away your ability to differentiate between them if you want to.

    If a less-strict comparison is desired, one can construct an expression using the or function to recognize several different values:

    [
      "or",
      ["equals", ["dataModel", "My.Path"], 0],
      ["equals", ["dataModel", "My.Path"], false],
      ["equals", ["dataModel", "My.Path"], null],
      ["equals", ["dataModel", "My.Path"], ""]
    ]
    

    Additionally, note that conversion to boolean value allows for more alternatives than strings (as expected by equals). Given that the or function expects boolean values as arguments, and the values 0, false, and null are already accepted as boolean values, the following will function similarly to the expression above:

    ["or", ["dataModel", "My.Path"], ["equals", ["dataModel", "My.Path"], ""]]