为什么 .forEach 返回未定义? [英] Why is .forEach returning undefined?

问题描述

我知道这个主题已经有多个问题https://stackoverflow.com/search?q=%5Bjavascript%5D+return+forEach+undefined 但这些似乎都没有帮助我.

I know there already are multiple questions to this topic https://stackoverflow.com/search?q=%5Bjavascript%5D+return+forEach+undefined but none of this seemed to help me out.

所以我有以下数据:

 const testsMap = {
            0: ["just", "test"],
            1: ["bla", "asdf"]
        }

 const testArray = [{
    id: "1",
    segments: null,
    tests: [{
            id: "1",
            segments: "1"
        },
        {
            id: "2",
            segments: "0"
        }
    ]
},
{
    id: "2",
    segments: "1",
    tutorials: [{
            id: "1",
            segments: "1"
        },
        {
            id: "2",
            segments: "0"
        }
    ]
}];

我想使用 .map() 或 .reduce 的输出 实现什么，因为我不想要一个新数组，我只想覆盖现有的，如下:

What I want to achieve with the output without using .map() or .reduce since I do not want a new array, I just want to overwrite the existing one, is the following:

[{
    display: true,
    id: "1",
    segments: null,
    tests: [{
            display: true,
            id: "1",
            segments: "1",
            newSegments: ["bla", "asdf"]
        },
        {
            display: true,
            id: "2",
            segments: "0",
            newSegments: ["just", "test"]
        }
    ]
},
{
    display: false,
    id: "2",
    segments: "1",
    tutorials: [{
            id: "1",
            segments: "1"
        },
        {
            id: "2",
            segments: "2"
        }
    ]
}];

我的函数看起来像这样 - 请注意它有一些你可以忽略的辅助 fns - 只是 fn 返回 undefined:

The function I have looks something like this - please note that it has some helper fns which you can ignore - it's just about that the fn returns undefined:

function SOtest () {
  const returnedValue = testArray.forEach(test => {
    test.newSegments = test.segments ? testsMap[test.segments] : [];
    test.display = helperFn(); // will add true/false to the test prop

    if (test.display) {
      test.tests.map(t => {
        t.newSegments = t.segments ? testsMap[t.segments] : [];
        t.display = helperFn(); // will add true/false to the test prop
      })
    }
    return test;
  })
  return returnedValue;
}

现在 forEach 本身在控制台中自行执行时可以正常工作 - 但只要我想返回它，它就等于 undefined.

Now the forEach itself works just fine when executed by itself in the console - but as soon as I want to return it, it equals undefined.

我错过了什么?

推荐答案

forEach 不返回任何内容.它只是循环元素，循环时你可以改变元素数据

forEach doesn't return anything. It just loops through elements and while looping you can change element data

因此您可以将函数 SOtest 更改为

And so you can change your function SOtest to

function SOtest () {
  testArray.forEach(test => {
    test.newSegments = test.segments ? testsMap[test.segments] : [];
    test.display = helperFn(); // will add true/false to the test prop

    if (test.display) {
      test.tests.map(t => {
        t.newSegments = t.segments ? testsMap[t.segments] : [];
        t.display = helperFn(); // will add true/false to the test prop
      })
    }
  })
  return testArray;
}

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