淺談var,let,const

        console.log(num);
        var num = 10; // 打印 undefined, 而不是報錯， 這說明var將變量的聲明提升

        // var num;
        num = 10;
        console.log(num); // 打印 10, var 將變量num的聲明提升到最頂層
        var num; 

       for(var i=0;i<5;i++){
        console.log("222222",i);
       }
       console.log("ssss",i) //由于用var聲明的i，所以在這里能獲取到for循環中的i,產生了變量污染

        console.log(num1);
        let num1 = 10; //Uncaught ReferenceError: Cannot access 'num1' before initialization

       for(let i=0;i<5;i++){
        console.log("222222",i);
       }
       console.log("ssss",i) //Uncaught ReferenceError: i is not defined 這是正常的錯誤

    const num = 10
    num = 11 // TypeError: Assignment to constant variable.
    console.log("num:",num)

        const num; 
        num = 10; // Uncaught SyntaxError: Missing initializer in const declaration
        console.log(num)