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varwindow.b = "hi";b; // "hi"delete b; // trueb; // ReferenceError: b is not defined(function(){c = "hi"}());c; // "hi"delete c; // truec; // ReferenceError: c is not definedvar a = "hi";a; // "hi"delete a; // falsea; // "hi"

Answer 1

var x = 1

undefined

Object.getOwnPropertyDescriptor(window,'x')

Object {value: 1, writable: true, enumerable: true, configurable: false}

window.y = 1

1

Object.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。