92 lines
1.6 KiB
Markdown
92 lines
1.6 KiB
Markdown
# js info
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### 预编译
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链接：
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* https://juejin.cn/post/6916046341131599879
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* https://juejin.cn/post/6896445621273083912
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demo1:
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```
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function f() {
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console.log(aa); // undefined
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var aa = 5;
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console.log(aa); // 5
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}
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f();
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```
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demo2:
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```
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var scope = 'global';
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function t() {
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console.log(scope); // undefined
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var scope = 'local';
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console.log(scope); // local
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}
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t();
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console.log(scope); // global
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```
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demo3:
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```
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console.log(b) //undefined 变量提升
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var b =2;
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```
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demo4
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```
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console.log(foo)
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function foo(){
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}
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var foo =1
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```
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### 作用域
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demo1:
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```
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function zxxFn () {
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zxxs = 2
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}
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var zxx = 1
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console.log(window.zxx) // 1
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// console.log(zxxs) 未定义
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zxxFn() // 执行后zxxs成为全局变量
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console.log(zxxs) // 2
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```
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```
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var zxx = 'zxx is a good girl'
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function zxxFn () {
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console.log(zxx)
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var zxx = 'zxx is a great girl'
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console.log(zxx)
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zxx = 'very good'
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console.log(zxx)
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}
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console.log(zxx)
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zxxFn()
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console.log(zxx)
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// 依次输出 1. zxx is a good girl 2. undefined 3. zxx is a great girl
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// 4. very good 5.zxx is a good girl
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```
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```
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zxxAge = 'zxx is 18 years old'
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function zxxFn () {
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console.log(zxxAge)
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var zxxAge = 'zxx is 8 years old'
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var zxxSub = 'zxx is 25 years old'
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console.log(zxxAge) // zxx is 8 years old
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// console.log(zxxSub) // zxxSub is not defined
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function zxxFnSub () {
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var zxxSub = 'zxx is 18 years old'
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console.log(zxxSub) // zxx is 18 years old
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console.log(zxxAge) // zxxSub is not defined
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}
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zxxFnSub()
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}
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zxxFn()
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```
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