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函数声明的提升、变量提升(hoisting)
在javascript中函数的声明以及变量的声明都会被提升到最顶部:
-
定义函数:
a.函数声明:
function functionName (arg) {} //这种格式的为函数声明
b.函数表达式:
// 这种格式的是函数表达式,是匿名函数
var variableName = function () {}
// 也可以如下
var variableName = function functionName () {} -
变量提升:
x = 5;
console.log(x)
var x
// 但是变量的初始化不会进行提升(如下会报错)
console.log(a)
var a = 3
3.函数声明和函数表达式的区别:
函数声明会提升,即:可以先使用后声明(在严格模式下则也必须先声明再使用)
函数表达式必须先定义再使用
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