关于javascript:varlet的区别

var申明晋升

console.log(name)  //土豆var name = '土豆';

应用var申明的变量会主动晋升到函数作用域的顶部

function foo(){    console.log(name);    var name = "土豆";}foo()  //undefined//等价于function foo(){    var name;    console.log(name);    name = "土豆";}foo(); //undefined

console.log(name)  //ReferenceError name没有被定义let name ="土豆";

而应用let定义的name不会被晋升，报出ReferenceError的谬误；

var能够反复申明同一个变量

var name = "番茄";var name = "西瓜";var name = "土豆";console.log(name);//土豆

而应用let反复申明同一个变量会报错。

var name = "土豆";let name = "土豆";console.log(name);//'name' has already been declared

let name = "土豆";var name = "土豆";console.log(name);//Cannot redeclare block-scoped variable 'name'.

var全局申明

var name = "土豆";console.log(window.name);//土豆let age = "24";console.log(window.age);  //undefined

应用var定义的变量会被挂载到window上，成为window对象的属性，而应用let不会。

作用域

if(true){    var name = "土豆";    console.log(name);}console.log(name);//土豆//土豆if(true){    let age = 24;    console.log(age);}console.log(age);//24//undefined

应用var申明的范畴是函数作用域，应用let申明的范畴是块作用域。