> For the complete documentation index, see [llms.txt](https://easonwang.gitbook.io/web_advance/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://easonwang.gitbook.io/web_advance/es6-es7-es8/es6_symbol.md).

# ES6 Symbol

用途:讓Object中的key名稱不會被之後取相同名字的key覆蓋

```
var a = {}

var g = Symbol('aa')

var v = Symbol('aa')

a[g] = 12
a[v] = 15


Symbol(): 13

Symbol(aa):13453453
Symbol(aa): 12
```

之後必須用a\[g]來取值，不可用a.g

## 實用處

```javascript
const actions = {
  fetch: "FETCH",
  get: "GET" 
}

// 以前的寫法可改為

const actions = {
  fetch: Symbol(),
  get: Symbol()
}


switch ...
case: action.fetch
....
```