今天我们来看五个案例，深入了解作用域提升相关的问题。
案例一
var n = 100;
function foo(){
n = 200;
}
foo()
console.log(n)这里输出什么？这里输出200
案例二
function foo(){
console.log(n)
var n = 200;
console.log(n)
}
var n = 100;
foo();第一次打印undefined，第二次打印200.
案例三
var n = 100;
function foo1(){
console.log(n)
}
function foo2(){
var n = 200;
console.log(n)
foo1();
}
foo2();
console.log(n);这里先打印200，然后再打印100，最后打印100.
案例四
var a = 100;
function foo(){
console.log(a)
return
var a = 100
}
foo()这里我们先打印undefined
案例五
function foo(){
var a = b = 100;
}
foo();
console.log(a);
console.log(b);这里打印出来第一行打印报错，如果我们注释console。log(a)只打印b的话就是100.
感谢大家观看！
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