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JavaScript

Turandeep Munday
Turandeep Munday
6,047 Points

Why can i not increment values in an array using for of even when using let

let array = [1,2,3];
console.log(array);

for ( let arr of array ) {
   arr ++;
   console.log(arr)
   console.log(array)
}; 

Is this because arr will loop through the values but these are in local scope and don't affect the array lietral?
Turandeep Munday
Turandeep Munday
6,047 Points

I was expecting the array to be returned with all values in the array added by +1 but this wasn't the case.

2 Answers

Steven Parker
Steven Parker
230,248 Points

You're right, the loop variable "arr" is local in scope and only contains a copy of the current array element's value. So incrementing it will not affect the original array.

Modifying the array is easily done in a conventional loop:

for (let i = 0; i < array.length; i++) {
  array[i]++;
} 

Or using the "map" method:

array = array.map(arr => ++arr);  // note: post-increment won't work here
Turandeep Munday
Turandeep Munday
6,047 Points

Thanks - I assume it's not possible to change the array values in a let.. of loop?

Steven Parker
Steven Parker
230,248 Points

Not by modifying the loop variable. That's why a different kind of loop would make more sense.