JavaScript property lazy build lazy initialization getter method

lazybuild.js

var seq = 0;
var Foo = function () {
    this.seq = ++ seq;
};
var Bar = function () {
    this.fooB = new Foo();
};
Bar.prototype = {
    fooA: new Foo(), // shared
    get fooC() {
        return this._fooC = this._fooC || new Foo(); // lazy build
    }
};

var bar1 = new Bar();
var bar2 = new Bar();
var bar3 = new Bar();

console.log('bar1', bar1.fooA.seq, bar1.fooB.seq, bar1.fooC.seq); // 1 2 5
console.log('bar3', bar3.fooA.seq, bar3.fooB.seq, bar3.fooC.seq); // 1 4 6
console.log('bar2', bar2.fooA.seq, bar2.fooB.seq, bar2.fooC.seq); // 1 3 7

2013-01-12
JavaScript プロパティ lazy build 遅延初期化 getter メソッド
http://kawanet.hatenablog.com/entries/2013/01/12