ESNext Class

Jackie Park

2 min read

·

Sep 30, 2016

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esnext class

es5

class-like

function Point(x, y) {
  this.x = x;
  this.y = y;
}Point.prototype.toString = function() {
  return '(' + this.x + ', ' + this.y + ')';
}var p = new Point(2, 2);
p.toString();console.log(p instanceof Point); // true
console.log(p instanceof Object); // true

es6

class

class Point {
  constructor(x, y) {
    this.x = x;
    this.y = y;
  }
  toString() {
    return '(' + this.x + ', ' + this.y + ')';
  }
}let p = new Point(2, 2);
p.toString();
console.log(p instanceof Point); // true
console.log(p instanceof Object); // true
console.log(typeof Point); // function
console.log(typeof Point.prototype.toString); // function

compatable class

• class is not hoisted, see temporal dead zone
• class runs in strict mode
• all methods are noe enumerable
• class will throw an error without new operator

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'use strict';var _createClass = function() {
    function defineProperties(target, props) {
        for (var i = 0; i < props.length; i++) {
            var descriptor = props[i];
            descriptor.enumerable = descriptor.enumerable || false;
            descriptor.configurable = true;
            if ("value" in descriptor) descriptor.writable = true;
            Object.defineProperty(target, descriptor.key, descriptor);
        }
    }
    return function(Constructor, protoProps, staticProps) {
        if (protoProps) defineProperties(Constructor.prototype, protoProps);
        if (staticProps) defineProperties(Constructor, staticProps);
        return Constructor;
    };
}();function _classCallCheck(instance, Constructor) {
    if (!(instance instanceof Constructor)) {
        throw new TypeError("Cannot call a class as a function");
    }
}var Point = function() {
    function Point(x, y) {
        _classCallCheck(this, Point);        this.x = x;
        this.y = y;
    }    _createClass(Point, [{
        key: 'toString',
        value: function toString() {
            return '(' + this.x + ', ' + this.y + ')';
        }
    }]);    return Point;
}();let Point = (function() {    "use strict";    const Point = function(name) {        // make sure the function was called with new
        if (typeof new.target === "undefined") {
            throw new Error("Constructor must be called with new.");
        }        this.name = name;
    }    Object.defineProperty(Point.prototype, "toString", {
        value: function() {            // make sure the method wasn't called with new
            if (typeof new.target !== "undefined") {
                throw new Error("Method cannot be called with new.");
            }            console.log(this.name);
        },
        enumerable: false,
        writable: true,
        configurable: true
    });    return Point;
}());