Comments (3)
答案
5 Error, a is not defined
解析
在这个立即执行函数表达式(IIFE)中包括两个赋值操作,其中a
使用var
关键字进行声明,因此其属于函数内部的局部变量(仅存在于函数中),相反,b
被分配到全局命名空间。
另一个需要注意的是,这里没有在函数内部使用严格模式(use strict
;)。如果启用了严格模式,代码会在输出 b 时报错Uncaught ReferenceError: b is not defined
,需要记住的是,严格模式要求你显式的引用全局作用域。因此,你需要写成:
(function () {
"use strict";
var a = (window.b = 5);
})();
console.log(b);
再看一个
(function() {
'use strict';
var a = b = 5;
})();
console.log(b); //Uncaught ReferenceError: b is not defined
/*---------------------------*/
(function() {
'use strict';
var a = window.b = 5;
})();
console.log(b); // 5
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(function() {
'use strict';
var a = b = 5;
})();
console.log(b);
但是在chrome控制台,输出的也是5 ???
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(function() { 'use strict'; var a = b = 5; })();
console.log(b); 但是在chrome控制台,输出的也是5 ???
您应该是运行过上一段代码,保留着全局的 b 变量。 换一个变量名就可以得出正确结果了
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