一、迴圈與迭代 Iteration

倘若使用手動迭代的方式，比如`(for i=0, i<9, i++)`,那麼程式設計就會陷入到dirty-details之中。

ES6標準化了specifi-protocol的iterator-pattern.

    // an array is an iterable    var arr = [ 10, 20, 30 ];    for (let val of arr) {        console.log(`Array value: ${ val }`);    }      //map and destruction    var buttonNames = new Map();    buttonNames.set(btn1,"Button 1");    buttonNames.set(btn2,"Button 2");        for (let [btn,btnName] of buttonNames) {        btn.addEventListener("click",function onClick(){            console.log(`Clicked ${ btnName }`);        });    }    // values, keys and entries     for (let btnName of buttonNames.values()) {        console.log(btnName);    }    // Button 1    // Button 2

二、閉包 Closure

Closure的定義：

  Closure is when a function remembers and continues to access variables  from outside its scope, even when the function is executed in a  different scope.

示例應用：

    function counter(step = 1) {        var count = 0;        return function increaseCount(){            count = count + step;            return count;        };    }    var incBy1 = counter(1);    var incBy3 = counter(3);        incBy1();       // 1    incBy1();       // 2        incBy3();       // 3    incBy3();       // 6    incByf3();       // 9

在event中的應用：

    for (let [idx,btn] of buttons.entries()) {        btn.addEventListener("click",function onClick(){           console.log(`Clicked on button (${ idx })!`);        });    }

三、this關鍵詞的function

Function內的this關鍵詞要看其execution-context，首先定義 this-aware的function。

    function classroom(teacher) {        return function study() {            console.log(                `${ teacher } says to study ${ this.topic }`            );        };    }    var assignment = classroom("gaowei");

然後將其分派到object中：

    var homework = {        topic: "JS",        assignment: assignment    };    homework.assignment();    // gaowei says to study JS 

另外一種調取方法：

    var otherHomework = {        topic: "Math"    };    assignment.call(otherHomework);    // Kyle says to study Math

四、Prototype

定義homework，雖有隻有topic這一個property，但卻linkage-connect到Object.prototype的多個屬性。

> let homework = {... topic: "JS",... }undefined> homework.homework.__defineGetter__      homework.__defineSetter__homework.__lookupGetter__      homework.__lookupSetter__homework.__proto__             homework.constructorhomework.hasOwnProperty        homework.isPrototypeOfhomework.propertyIsEnumerable  homework.toLocaleStringhomework.toString              homework.valueOfhomework.topic

五、Object Linkage

檢視下面的案例：

    var homework = {        topic: "JS"    };    var otherHomework = Object.create(homework);        otherHomework.topic;   // "JS"    homework.topic;    // "JS"    otherHomework.topic;    // "JS"        otherHomework.topic = "Math";    otherHomewokrk.topic;    // "Math"        homework.topic;    // "JS" -- not "Math"