Unable to push elements in a new array in javascript

Question

I am writing a very easy function where I am checking the even numbers from an array of integer and adding those even numbers into the new array. But after getting the even numbers from first array when I am trying to push into second array its showing undefined.

const arr = [1,2,3,4,5,6];
const newArr = [];

const loop = () => {
 for (var item of array) {
  if (item % 2 == 0) {
   console.log(item);
   newArr.push(item);
  }
 }
};

console.log(loop());

Output

2 4 6 undefined

Why new array is showing undefined.

You push to newArr but never do anything to it or print it — mousetail
– mousetail, Commented Jun 15, 2022 at 7:07
loop() has no return statement, therefore, it implicitly produces undefined. And when you log the return value of executing the function loop() you see this undefined in the console. — VLAZ
– VLAZ, Commented Jun 15, 2022 at 7:10
arr is defined: check ... newArr is defined: checked ... code iterates over array ... which is nowhere to be seen: check — Bravo
– Bravo, Commented Jun 15, 2022 at 7:10

nedoder · Accepted Answer · 2022-06-15 07:10:38Z

1

You can do it simply with forEach.

const arr = [1,2,3,4,5,6];
const newArr = [];


arr.forEach(item => {
  if (item % 2 == 0) {
   newArr.push(item);
  }
})

console.log(newArr);

answered Jun 15, 2022 at 7:10

nedoder

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1 Comment

Cerbrus Over a year ago

This doesn't explain why OP's code wasn't working, nor why your code does work.

Lars Hendriks · Accepted Answer · 2022-06-15 07:34:41Z

0

either return the newArray or execute the loop method and print the new Array.

The reason why you get undefined is because loop is currently a void operator and returning nothing. so if you want the loop method to return the array then the second code sample I showed is the better solution. if you just want to print the array then the first one does the trick.

const arr = [1,2,3,4,5,6];
const newArr = [];


arr.forEach(item => {
  if (item % 2 == 0) {
   newArr.push(item);
  }
})

console.log(newArr);

or

const arr = [1,2,3,4,5,6];

const loop = () => {
 const newArr = [];
 for (var item of arr) {
  if (item % 2 == 0) {
   console.log(item);
   newArr.push(item);
  }
 }
 return newArr
};
console.log(loop());

both will work.

edited Jun 15, 2022 at 7:34

answered Jun 15, 2022 at 7:10

Lars Hendriks

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5 Comments

Digvijay Singh Thakur Over a year ago

in your 2nd solution why have you put loop() inside console.log() even if inside loop() we have an return newArr used.

Cerbrus Over a year ago

"because loop is currently a void." You might want to reword that. @Digvijay: What else would you have put in the console.log?

Lars Hendriks Over a year ago

@Digvijay well i don't know exactly what your use case is for the loop method. i just thought it could've been your use case as your question has loop in the console log

Lars Hendriks Over a year ago

@Cerbrus hey, i tried to add some information. if you think I'm missing something, please edit so that I can approve it and maybe learn something aswell.

Cerbrus Over a year ago

That's a lot better! Note that users above 2k rep can't "suggest" edits, any more. Edits by those users just get applied :-)

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