角@NGRX中的三个点是什么意思 [英] Angular what's meaning of three dots in @NGRX

问题描述

这三个点到底是什么意思，为什么我需要它们?

what does mean exactly these three dots and why i need them ?

export function leadReducer(state: Lead[]= [], action: Action {
    switch(action.type){
        case ADD_LEAD:
            return [...state, action.payload];
        case REMOVE_LEAD:
            return state.filter(lead => lead.id !== action.payload.id )
}
}

推荐答案

这三个点称为传播算子来自Typescript(也来自 ES7 ).

The three dots are known as the spread operator from Typescript (also from ES7).

spread运算符返回数组的所有元素.就像您要分别编写每个元素一样:

The spread operator return all elements of an array. Like you would write each element separately:

let myArr = [1, 2, 3];
return [1, 2, 3];
//is the same as:
return [...myArr];

这主要是语法糖，因为它是这样编译的:

This is mostly just syntactic sugar as it compiles this:

func(...args);

对此:

func.apply(null, args);

在您的情况下，将其编译为以下内容:

In your case this gets compiled to this:

return [...state, action.payload];
//gets compiled to this:
return state.concat([action.payload]);

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