Flipping the script: Array reversal in JavaScript

After researching this topic on multiple platforms including SO, I came across a solution in Eloquent JavaScript that caught my attention. Here is the code snippet that I experimented with:

function reversedArray(array) {
    let reversedArray = [];
    for (let i = 0; i <= array.length; i++) {
        reversedArray.push(array[array.length - i]);
    }
    return reversedArray;
}
let arr = [
    1,
    2,
    3,
    4
];
console.log(arr);
console.log(reversedArray(arr));

The output of this code was unexpected as it showed:

> 1,2,3,4
> ,4,3,2,1

This indicates that the reversed array has one extra element than the original array. To fix this issue, I modified the code to remove the redundant first element from the reversed array:

function reversedArray(array) {
    let reversedArray = [];
    for (let i = 0; i <= array.length; i++) {
        reversedArray.push(array[array.length - i]);
    }
    reversedArray.shift();
    return reversedArray;
}
let arr = [
    1,
    2,
    3,
    4
];
console.log(arr);
console.log(reversedArray(arr));

Upon running this updated code, the output appeared exactly as intended:

> 1,2,3,4
> 4,3,2,1

As someone new to JS, I am puzzled by why the array length increases when using my initial function. Any insights on this matter would be highly appreciated. I want to understand the underlying concept rather than just fixing the issue. Thank you!

Answer №1

By reversing the loop direction, you can avoid the need for index subtraction.

const reverseArray = (arr) => {
  const resultArr = [];
  for (let j = arr.length - 1; j >= 0; j--) {
    resultArr.push(arr[j]);
  }
  return resultArr;
};

console.log(reverseArray([5, 4, 3, 2, 1]));

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