forEach is returning undefined

Question

I want my foreach() to loop through an array of maps and check if the type value matches. If not return the else statement.

Function

function checkCars(carData) {
        const cars = carData.models;

        models.forEach(model => {
            if (model.type === 'Toyota' || model.type === 'Hyundai') {
                return "Type A";
            } else {
                return "Type B";
            }
        });
    }

Database

"models": [
  {type: "Toyota"}
  {type: "Hyundai"}
  {type: "Audi"}
  {type: "VW"}
]

Use another variable to hold type and return that outside for each in function — MJN, Jan 19 '20 at 05:29
Does this answer your question? [Can forEach in JavaScript make a return?](https://stackoverflow.com/questions/32041912/can-foreach-in-javascript-make-a-return) — user2864740, Jan 19 '20 at 06:27

Mamun · Accepted Answer · 2020-01-19T05:35:06.710

4

The return value of Array.prototype.forEach() is undefined, you can not return anything explicitly from forEach().

You can try with Array.prototype.map() instead:

The map() method creates a new array populated with the results of calling a provided function on every element in the calling array.

function checkCars(carData) {
  const cars = carData.models;

  return models.map(model => {
    if (model.type === 'Toyota' || model.type === 'Hyundai') {
      return "Type A";
    } else {
      return "Type B";
    }
  });
}

edited Jan 19 '20 at 05:35

answered Jan 19 '20 at 05:26

Mamun

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What about breaking the loop when the first `if` is true? – aszet Jan 19 '20 at 05:35
1

@aszet, you can not even brake the loop, they are bound to execute for all the elements in the array. To break the loop you have to use simple *for* loop. – Mamun Jan 19 '20 at 05:38
@aszet If you want some, use `.some()`, if you want all use `.every()`. See [documentation](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Array) for examples. – some Jan 19 '20 at 05:45

score 2 · Answer 2 · answered Jan 19 '20 at 05:29

2

forEach has no return value. You should use map function to change the element's types.

answered Jan 19 '20 at 05:29

Tugrul Emre Atalay

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score 1 · Answer 3 · answered Jan 19 '20 at 05:28

1

If you want to transform the array, you want map:

function checkCars(carData) {
  const cars = carData.models;

  return models.map(model => {
    if (model.type === 'Toyota' || model.type === 'Hyundai') {
      return "Type A";
    } else {
      return "Type B";
    }
  });
}

answered Jan 19 '20 at 05:28

tadman

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You're going to have to be more specific about what the issue is, then. What output *do* you want? – tadman Jan 19 '20 at 05:31

score 0 · Answer 4 · answered Jan 19 '20 at 05:30

You can use something like this:

function checkCars(carData) {
        const cars = carData.models;
        let type = "Type A"
        models.forEach(model => {
            if (model.type !== 'Toyota' && model.type !== 'Hyundai') {
                type = "Type B";
            }
        });
        return type
    }

forEach is returning undefined

4 Answers4

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