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                ??碼云GVP開源項目 12k star Uniapp+ElementUI 功能強大 支持多語言、二開方便! 廣告
                # 字符串字面量類型 字符串字面量類型用來約束取值只能是某幾個字符串中的一個。 ## 簡單的例子 ```ts type EventNames = 'click' | 'scroll' | 'mousemove'; function handleEvent(ele: Element, event: EventNames) { // do something } handleEvent(document.getElementById('hello'), 'scroll'); // 沒問題 handleEvent(document.getElementById('world'), 'dbclick'); // 報錯,event 不能為 'dbclick' // index.ts(7,47): error TS2345: Argument of type '"dbclick"' is not assignable to parameter of type 'EventNames'. ``` 上例中,我們使用 `type` 定了一個字符串字面量類型 `EventNames`,它只能取三種字符串中的一種。 注意,**類型別名與字符串字面量類型都是使用 `type` 進行定義。** ## 參考 - [Advanced Types # Type Aliases](http://www.typescriptlang.org/docs/handbook/advanced-types.html#string-literal-types)([中文版](https://zhongsp.gitbooks.io/typescript-handbook/content/doc/handbook/Advanced%20Types.html#字符串字面量類型)) --- - [上一章:類型別名](type-aliases.md) - [下一章:元組](tuple.md)
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