Is there a way in JavaScript to retrieve the indexes of undefined array elements without using a loop? Possibly utilizing a combination of map, filter, and indexOf?
I have a loop solution that I'm seeking an alternative for - something more concise, like a one-liner:
const sourceArray = [,1,undefined,3];
const filteredArray = [];
for (let i = 0; i < sourceArray.length; i++) {
if (sourceArray[i] === undefined) filteredArray.push(i);
}
console.log(filteredArray); // [0,2]
If you want to create a new array based on specific values and indices, you can use the Array.from method in JavaScript.
Array.from is particularly useful for generating arrays without any gaps, which can then be easily filtered.
const
originalArray = [, 1, undefined, 3],
newArray = Array
.from(originalArray, (_, index) => index)
.filter(index => originalArray[index] === undefined);
console.log(newArray); // [0, 2]Here is an example of a less than ideal solution, provided for comparison:
let arr1 = [0, , 2, undefined, 4, , 6];
let arr2 = [];
let arr3 = arr1;
let index;
while ((index = arr3.findIndex(val => val === undefined)) > -1) {
if (arr2.length)
arr2.push(arr2.at(-1) + index + 1);
else
arr2.push(index);
arr3 = arr3.slice(index + 1);
}
console.log(arr2);
Not the most efficient code, right? I was intrigued by the fact that findIndex() does not ignore empty array elements like indexOf() does. However, it only identifies the first instance of a value, necessitating slicing the array in each iteration to make it function. I wrote and tested it on jsfiddle just to observe its performance. The outcome speaks volumes.
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