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    type-check
    DefinitelyTyped icon, indicating that this package has TypeScript declarations provided by the separate @types/type-check package

    0.4.0 • Public • Published

    type-check Build Status

    type-check is a library which allows you to check the types of JavaScript values at runtime with a Haskell like type syntax. It is great for checking external input, for testing, or even for adding a bit of safety to your internal code. It is a major component of levn. MIT license. Version 0.4.0. Check out the demo.

    For updates on type-check, follow me on twitter.

    npm install type-check
    

    Quick Examples

    // Basic types:
    var typeCheck = require('type-check').typeCheck;
    typeCheck('Number', 1);               // true
    typeCheck('Number', 'str');           // false
    typeCheck('Error', new Error);        // true
    typeCheck('Undefined', undefined);    // true
     
    // Comment
    typeCheck('count::Number', 1);        // true
     
    // One type OR another type:
    typeCheck('Number | String', 2);      // true
    typeCheck('Number | String', 'str');  // true
     
    // Wildcard, matches all types:
    typeCheck('*', 2) // true
     
    // Array, all elements of a single type:
    typeCheck('[Number]', [1, 2, 3]);                // true
    typeCheck('[Number]', [1, 'str', 3]);            // false
     
    // Tuples, or fixed length arrays with elements of different types:
    typeCheck('(String, Number)', ['str', 2]);       // true
    typeCheck('(String, Number)', ['str']);          // false
    typeCheck('(String, Number)', ['str', 2, 5]);    // false
     
    // Object properties:
    typeCheck('{x: Number, y: Boolean}', {x: 2, y: false});             // true
    typeCheck('{x: Number, y: Boolean}',       {x: 2});                 // false
    typeCheck('{x: Number, y: Maybe Boolean}', {x: 2});                 // true
    typeCheck('{x: Number, y: Boolean}',      {x: 2, y: false, z: 3});  // false
    typeCheck('{x: Number, y: Boolean, ...}', {x: 2, y: false, z: 3});  // true
     
    // A particular type AND object properties:
    typeCheck('RegExp{source: String, ...}', /re/i);          // true
    typeCheck('RegExp{source: String, ...}', {source: 're'}); // false
     
    // Custom types:
    var opt = {customTypes:
      {Even: { typeOf: 'Number', validate: function(x) { return x % 2 === 0; }}}};
    typeCheck('Even', 2, opt); // true
     
    // Nested:
    var type = '{a: (String, [Number], {y: Array, ...}), b: Error{message: String, ...}}'
    typeCheck(type, {a: ['hi', [1, 2, 3], {y: [1, 'ms']}], b: new Error('oh no')}); // true

    Check out the type syntax format and guide.

    Usage

    require('type-check'); returns an object that exposes four properties. VERSION is the current version of the library as a string. typeCheck, parseType, and parsedTypeCheck are functions.

    // typeCheck(type, input, options);
    typeCheck('Number', 2);               // true
     
    // parseType(type);
    var parsedType = parseType('Number'); // object
     
    // parsedTypeCheck(parsedType, input, options);
    parsedTypeCheck(parsedType, 2);       // true

    typeCheck(type, input, options)

    typeCheck checks a JavaScript value input against type written in the type format (and taking account the optional options) and returns whether the input matches the type.

    arguments
    • type - String - the type written in the type format which to check against
    • input - * - any JavaScript value, which is to be checked against the type
    • options - Maybe Object - an optional parameter specifying additional options, currently the only available option is specifying custom types
    returns

    Boolean - whether the input matches the type

    example
    typeCheck('Number', 2); // true

    parseType(type)

    parseType parses string type written in the type format into an object representing the parsed type.

    arguments
    • type - String - the type written in the type format which to parse
    returns

    Object - an object in the parsed type format representing the parsed type

    example
    parseType('Number'); // [{type: 'Number'}]

    parsedTypeCheck(parsedType, input, options)

    parsedTypeCheck checks a JavaScript value input against parsed type in the parsed type format (and taking account the optional options) and returns whether the input matches the type. Use this in conjunction with parseType if you are going to use a type more than once.

    arguments
    • type - Object - the type in the parsed type format which to check against
    • input - * - any JavaScript value, which is to be checked against the type
    • options - Maybe Object - an optional parameter specifying additional options, currently the only available option is specifying custom types
    returns

    Boolean - whether the input matches the type

    example
    parsedTypeCheck([{type: 'Number'}], 2); // true
    var parsedType = parseType('String');
    parsedTypeCheck(parsedType, 'str');     // true
    ## Type Format

    Syntax

    White space is ignored. The root node is a Types.

    • Identifier = [\$\w]+ - a group of any lower or upper case letters, numbers, underscores, or dollar signs - eg. String
    • Type = an Identifier, an Identifier followed by a Structure, just a Structure, or a wildcard * - eg. String, Object{x: Number}, {x: Number}, Array{0: String, 1: Boolean, length: Number}, *
    • Types = optionally a comment (an Identifier followed by a ::), optionally the identifier Maybe, one or more Type, separated by | - eg. Number, String | Date, Maybe Number, Maybe Boolean | String
    • Structure = Fields, or a Tuple, or an Array - eg. {x: Number}, (String, Number), [Date]
    • Fields = a {, followed one or more Field separated by a comma , (trailing comma , is permitted), optionally an ... (always preceded by a comma ,), followed by a } - eg. {x: Number, y: String}, {k: Function, ...}
    • Field = an Identifier, followed by a colon :, followed by Types - eg. x: Date | String, y: Boolean
    • Tuple = a (, followed by one or more Types separated by a comma , (trailing comma , is permitted), followed by a ) - eg (Date), (Number, Date)
    • Array = a [ followed by exactly one Types followed by a ] - eg. [Boolean], [Boolean | Null]

    Guide

    type-check uses Object.toString to find out the basic type of a value. Specifically,

    {}.toString.call(VALUE).slice(8, -1)
    {}.toString.call(true).slice(8, -1) // 'Boolean'

    A basic type, eg. Number, uses this check. This is much more versatile than using typeof - for example, with document, typeof produces 'object' which isn't that useful, and our technique produces 'HTMLDocument'.

    You may check for multiple types by separating types with a |. The checker proceeds from left to right, and passes if the value is any of the types - eg. String | Boolean first checks if the value is a string, and then if it is a boolean. If it is none of those, then it returns false.

    Adding a Maybe in front of a list of multiple types is the same as also checking for Null and Undefined - eg. Maybe String is equivalent to Undefined | Null | String.

    You may add a comment to remind you of what the type is for by following an identifier with a :: before a type (or multiple types). The comment is simply thrown out.

    The wildcard * matches all types.

    There are three types of structures for checking the contents of a value: 'fields', 'tuple', and 'array'.

    If used by itself, a 'fields' structure will pass with any type of object as long as it is an instance of Object and the properties pass - this allows for duck typing - eg. {x: Boolean}.

    To check if the properties pass, and the value is of a certain type, you can specify the type - eg. Error{message: String}.

    If you want to make a field optional, you can simply use Maybe - eg. {x: Boolean, y: Maybe String} will still pass if y is undefined (or null).

    If you don't care if the value has properties beyond what you have specified, you can use the 'etc' operator ... - eg. {x: Boolean, ...} will match an object with an x property that is a boolean, and with zero or more other properties.

    For an array, you must specify one or more types (separated by |) - it will pass for something of any length as long as each element passes the types provided - eg. [Number], [Number | String].

    A tuple checks for a fixed number of elements, each of a potentially different type. Each element is separated by a comma - eg. (String, Number).

    An array and tuple structure check that the value is of type Array by default, but if another type is specified, they will check for that instead - eg. Int32Array[Number]. You can use the wildcard * to search for any type at all.

    Check out the type precedence library for type-check.

    Options

    Options is an object. It is an optional parameter to the typeCheck and parsedTypeCheck functions. The only current option is customTypes.

    ### Custom Types

    Example:

    var options = {
      customTypes: {
        Even: {
          typeOf: 'Number',
          validate: function(x) {
            return x % 2 === 0;
          }
        }
      }
    };
    typeCheck('Even', 2, options); // true
    typeCheck('Even', 3, options); // false

    customTypes allows you to set up custom types for validation. The value of this is an object. The keys of the object are the types you will be matching. Each value of the object will be an object having a typeOf property - a string, and validate property - a function.

    The typeOf property is the type the value should be (optional - if not set only validate will be used), and validate is a function which should return true if the value is of that type. validate receives one parameter, which is the value that we are checking.

    Technical About

    type-check is written in LiveScript - a language that compiles to JavaScript. It also uses the prelude.ls library.

    Install

    npm i type-check

    DownloadsWeekly Downloads

    24,825,026

    Version

    0.4.0

    License

    MIT

    Unpacked Size

    21.2 kB

    Total Files

    6

    Last publish

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