1.2.6.2.「typeof」、「instanceof」與搞清楚這是什麼

• typeof

  • 告訴你型別是甚麼

    var a = 3;
    //印出Number
    console.log(typeof a);
    
    var d = [];
    //印出Object
    console.log(typeof d);

• 用陣列在原型鍊上呼叫toString

  • call: 將this重新指向d並傳入其他參數, 並執行函數

  • toString會用this變數輸出他的值

    //印出[object Array]
    console.log(Object.prototype.toString.call(d));

• instanceof

  • 告訴你型別是甚麼

    var e = new Person('Jane');
    //true
    console.log(a instanceof Person);

• undefined, null

  • bug: typeof null是object

    //印出undefined
    console.log(typeof undefined);
    //印出object
    console.log(typeof null);

• empty function

    var z = function(){}
    //印出function
    console.log(typeof z);