What strategies can be utilized to address the absence of an element in an array iteration that is currently ongoing?

Currently, I am looping through an array of strings using forEach() method to check if each element's length is even or odd. If the length is even, I am removing it using splice().

Although my conditions seem correct, when I look at the input and output below, I notice that despite expecting the even, two-character word to be spliced out, it still appears in the return array.

Here's the code snippet:


function filterOddLengthWords(words) {
    words.forEach(function(element, index) {
        if (element.length % 2 === 0) {
            words.splice(index, 1);
        }
    })
    return words;
}

var output = filterOddLengthWords(['there', 'it', 'is', 'now']);
console.log(output); // --> [ 'there', 'is', 'now' ]

I can identify where the mistake lies but I need help figuring out how to rectify it. One possible solution could involve creating an empty array at the start of the function and then checking each element against the opposite condition, adding the positive results using push(). However, this method seems less efficient, so I'm hoping there might be a way to optimize my original approach. Thank you in advance for any advice.

Answer №1

When you splice an array, the index changes, whereas forEach loops through elements with their original indices.

Typically, when using splice, the iteration starts from the end so that if an item is removed, the index remains intact for items before it.


An alternative approach is to filter the array:

function filterOddLengthWords(words) {
    return words.filter(function(element) {
        return element.length % 2;
    });
}

var output = filterOddLengthWords(['there', 'it', 'is', 'now']);

console.log(output);

Answer №2

One issue with splicing the array in the context of the forEach() method is that when you perform a splice() operation on the array at index 1, causing the element it to shift to index 1, the subsequent element at index 2, which is is, gets moved to index 1 as well.

As a result, in the following iteration where the index is 2 within the callback function, the value at index 2 in the array becomes now instead of the intended is. Since now is evaluated as odd, it is preserved while the element is ends up being completely skipped over.

A more suitable approach would be to utilize Array.prototype.filter in this scenario, as it avoids altering the original array and instead gathers the valid outcomes into a fresh array.

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