为什么map会改变对象的数组? [英] Why does map mutate array of objects?

问题描述

可能是一个愚蠢的问题，但是为什么map会改变对象的数组.

Might be a stupid question, but why does map mutate array of objects.

var obj = {
  items: [{
    value: 1,
    selected: true
  }, {
    value: 2,
    selected: false
  }]
};

var items = obj.items.map(i => {
  if (i.value === 2) i.selected = true;
  return i;
});

console.log(obj);

推荐答案

映射数组时，它不是在创建对象的副本.它只是遍历数组.

When you map an array, it's not creating a copy of the object. It's just iterating over the array.

如果您不想变异对象，则必须创建该对象的副本:

If you don't want to mutate the object, you have to create a copy of the object:

var items = obj.items.map(item => {
    let i = JSON.parse(JSON.stringify(item))
    if (i.value === 2) i.selected = true;
    return i;
});

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