Question 51100 in Javascript Question posted in
A very good W3school tutorial can be found here.

Is this correct way to double each element of an array in JavaScript?

let array = [1,2,3,4,5,6]
for (element of array){
  array[array.indexOf(element)]= element*2
}
console.log(array)

This is the code I wrote for doubling each element of an array but the output I’m getting is
(6) [8, 2, 12, 4, 10, 6]

What is the mistake I’m making?

Could someone please tell the logical error that I am making here .

Tags:

3

Answers


  1. 0

    The first time around the loop you read the first item and get 1, then you find the first index which has the value 1 and you change it to 2 which leaves your array looking like: [2,2,3,4,5,6]

    The second time around the loop you read the second item and get 2, then you find the first index which has the value 2 and you change it to 4 which leaves your array looking like: [4,2,3,4,5,6]

    … and so on.

    Use a classic for loop and work based on the index.

    let array = [1,2,3,4,5,6]
for (let i = 0; i < array.length; i++){
  array[i]= array[i]*2
}
console.log(array)

    Also consider using map and overwriting array with a new array with the doubled values.

    let array = [1,2,3,4,5,6]
array = array.map(value => value * 2);
console.log(array);
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  2. 0

    If you really wanted to use your syntax, you could have cloned the array to fix.
    However, this answer is just for the example. It’s better to use solutions posted by Quentin.

    let array = [1,2,3,4,5,6]
let clonedArr = [...array];
for (element of clonedArr){
 array[clonedArr.indexOf(element)]= element*2
}
console.log(array)
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  3. 0

    Just to add to the collection of possible alternatives: if you really want to change the original array values then the following would work too:

    let array = [1,2,3,4,5,6]
array.forEach((_,i,a)=>a[i]*=2)
console.log(array)
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