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type Arr = number[] | string[];
type Arr1 = Array<string | number>;

const arr: Arr = [];
arr.push('123');

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请问,为何使用Arr1不报错,Arr报错?


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第一个类型表示这个数组要么全都是 number,要么全都是 string,二者不可交叉出现。

第二个类型表示这个数组每个元素要么是 number,要么是 string,二者可以交叉出现。

而你用第一种类型的时候:

const arr: Arr = [];

此时 arr 里到底应该必须只存 number 还是必须只 string 是未知的,所以后面你必须先断言才可以 push。


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