esnext-class

Write es6 like classes in es5 with a few more features

Cover some limitations to the current implementation of classes in es6:

• define properties
• use traits

Use

var newClass = require('esnext-class').newClass;

var A = newClass({
    constructor: function A(value) {
        this.initialized = value;
    }
});

var B = newClass({
    name: 'B',
    extends: A,

    constructor(value) {
        assert.strictEqual(this.constructor, B);
        this.bValue = value;
    }
});

Class special properties

• name: set the name of the class
• abstract: set the class as abstract
• constructor: this is the constructor of the class, like the constructor function in es6 classes
• extends: extends a class from another or from an object
• implements: light checks over expected implementations and warn eventually when something is missing
• prototype
• static: define static properties in the class
• with: an array of traits, objects with properties

Properties

Properties are defined in the prototype. If you want to set a property in the instance, use the constructor to do that. If you want to define a property in the object, use static.

Constant properties

You can set constant properties like this:

var A = newClass({
    name: 'A',
    constantProperty: newClass.const('myValue');
});

A.prototype.constantProperty = 'anotherValue'; // Error !

Lazy properties

var A = newClass({
    name: 'A',
    lazyProperty: newClass.lazy(() => 'expensive result');
});


var a = new A();
console.log(a.lazyProperty); // the result of the function is set in `a.lazyProperty`

Lazy constant properties

var A = newClass({
    name: 'A',
    lazyAndConstProperty: newClass.lazyConst(() => 'expensive result');
});


var a = new A();
console.log(a.lazyAndConstProperty); // the result of the function is set in `a.lazyProperty`

Note: both the prototype function and the instance property values are constants.