#Babel jsDoc runtime typecheck

Overview

This plugin will add runtime typecheck, based on jsDoc annotation. It transform code like this:

// from

/**
 * @param {Number} a
 * @returns {Number}
 * @typecheck
 */
function test(a) {
    return a;
}

// to

function test(a) {
    __executeTypeCheck__('test', 'a', a, 'Number');
    
    return __executeTypeCheck__('test', 'return', a, 'Number');
}

Result:

CAUTION: Use this plugin only in development, it will slow down your code (a lot of additional function calls and large helper function).

Motivation

Flow is good solution, but it adds custom syntax to javascript code and adding it to existing project is quite hard. IDE's like Webstorm has good support of jsDoc and can add cool code completion tips, based on users comments. So, with this plugin, you can easy start to use benefits of strong typing in javascript code without any pain. Using this plugin in development also will speed up development, because it will reduce number of weird errors and behaviors.

How to

Install

npm install babel-plugin-jsdoc-runtime-typecheck --save-dev

Use

.babelrc

{
    "plugins": ["jsdoc-runtime-typecheck"]
}

js code - global directive

// @typecheck

/**
 * @param {String} str
 * @returns {String}
 */
function makeMeLaugh(str) {
    return str + ' - ha-ha-ha!';
}

js code - local directive

/**
 * @param {String} str
 * @returns {String}
 * @typecheck
 */
function makeMeLaugh(str) {
    return str + ' - ha-ha-ha!';
}

Configure

useDirective

By default, plugin will only parse docs with special directive @typecheck, you can change it like this:

{
    "plugins": [
        ["jsdoc-runtime-typecheck",
            {
                //useDirective: 'typecheck' - this is default
                //useDirective: false - if you want to check all functions with jsDoc (useful for new projects)
                useDirective: 'makeMeHappy' - your custom directive
            }
        ]
    ]
}

Then, use it:

// @makeMeHappy 

// or

/**
 * @makeMeHappy 
 * @param {Number} a
 * @returns {Number}
 */

useStrict

You can enable strict mode - in this mode plugin throw compilation exception when it can find error by static analyze.

Setup:

{
    "plugins": [
        ["jsdoc-runtime-typecheck",
            {
                //useStrict: false - default
                useStrict: true
            }
        ]
    ]
}

Use:

Code:

/**
 * @param {Number} a
 * @param {Number} b
 * @returns {Number}
 * @typecheck
 */
function test(a, b, c) {
    return a + b + c;
}

Result in console:

SyntaxError: input.js: [TYPECHECK STRICT MODE]: Function argument type annotation missing.
   5 |  * @typecheck
   6 |  */
>  7 | function test(a, b, c) {
     |                     ^
   8 |     return a + b + c;
   9 | }
  10 | 

Supports:

jsDoc tags

• @params can be optional, supported declarations:

  • @param {*} name - no check

  • @param {Number=} name - optional

  • @param {Number} [name] - optional

  • @param {?Number} name

  • @param {!Number} name

  • @param {Number|String} id

  • @param {Array<Number>} collection - check every item in array

  • Check defined keys in Object:

    @param {Object} data 
    @param {Number} data.id
    @param {String} data.name
          
    //or
          
    @param {{id: Number, name: String}} data

  • @param {function(Array<Number>)} name - check type of function

• @returns or @return - type annotation are same as in params.

Language constructions

Function declaration

/**
 * @param {Number} a
 * @returns {Number}
 */
function myDeclaredFunction(a) {
    return a;
}

/**
 * @param {Number} a
 * @returns {Number}
 */
let myExpressionFunction = function(a) {
    return a;
};

/**
 * @param {Number} a
 * @returns {Number}
 */
let myArrowFunction = (a) => {
    return a;
};

/**
 * @param {Number} a
 * @returns {Number}
 * In this case it will transform body to "{ return a; }" block
 */
let myArrowExpressionFunction = (a) => a;

Object method

let myObject = {
    /**
     * @param {Number} a
     * @returns {Number}
     */
    myMethod(a) {
        return a;
    },
    
    /**
     * @param {Number} a
     * @returns {Number}
     * Will use object field name as function name ("myField" here)
     */
    myField: function(a) {
        return a;
    }
}

Class constructor and method

class MyClass {
    /**
     * @param {Number} a
     */
    constructor(a) {
        this._a = a;
    }
    
    /**
     * @param {Number} a
     * @returns {Number}
     */
    myMethod(a) {
       return a;
    }
    
    /**
     * @param {Number} a
     * @returns {Number}
     */
    static myStaticMethod(a) {
       return a;
    }
    
    /**
     * @param {Number} a
     */
    set a(a) {
        this._a = a;
    }
    
    /**
     * @returns {Number} a
     */
    get a() {
       return this._a;
    }
}