如何看待window.x和var x的区别

Question

很多文章都说，在内部省略var相当于声明了全局变量，如下代码显示这种写法与window.b更相似，而不是使用var

window.b = "hi";

b; // "hi"

delete b; // true

b; // ReferenceError: b is not defined

(function(){c = "hi"}());

c; // "hi"

delete c; // true

c; // ReferenceError: c is not defined

var a = "hi";

a; // "hi"

delete a; // false

a; // "hi"

Answer 1

var x = 1undefinedObject.getOwnPropertyDescriptor(window,'x')Object {value: 1, writable: true, enumerable: true, configurable: false}window.y = 11Object.getOwnPropertyDescriptor(window,'y')Object {value: 1, writable: true, enumerable: true, configurable: true}使用var声明的变量的configurable属性是false，就因为这。