I have an array and I want to convert the empty/undefined values to null. I have tried the following:
let arr = []
arr[1] = 2
arr[7] = 10
arr = arr.map(x => x || null)
console.log(arr)But the output of the snippet is not as desired:
[
undefined,
2,
undefined,
undefined,
undefined,
undefined,
undefined,
10
]
How do I replace these undefined values with nulls?
Note: Both vanilla JS and Lodash answers are acceptable.
What you have will work for an array that has undefined elements in it, but not for a sparse array with holes in it, because map doesn't visit the holes in a sparse array; instead, the resulting array just has holes in the same places.
If you want to map the holes as well, you can use Array.from with its mapping callback:
let arr = [];
arr[1] = 2;
arr[7] = 10;
arr = Array.from(arr, x => x || null);
console.log(arr);Unlike map, Array.from will go through all indexes of the array, including holes, passing undefined as x for the holes in the array to the mapping callback.
Another option is a simple for-of loop, because iteration visits holes in sparse arrays (which is why Array.from works above):
let arr = [];
arr[1] = 2;
arr[7] = 10;
const newArr = [];
for (const value of arr) {
newArr.push(value || null);
}
arr = newArr;
console.log(arr);Note that x || null will replace all falsy values with null (including 0 and "", which often trips people up). To just replace undefined, use x ?? null instead:
let arr = [];
arr[1] = 2;
arr[7] = 10;
arr = Array.from(arr, x => x ?? null);
console.log(arr);or
let arr = [];
arr[1] = 2;
arr[7] = 10;
const newArr = [];
for (const value of arr) {
newArr.push(value ?? null);
}
arr = newArr;
console.log(arr);x ?? y (nullish coalescing) is like x || y but only uses y if x evaluates to undefined or null.
Try something very basic:
let arr = [];
arr[1] = 2; arr[7] = 10;
for(let i=0; i< arr.length; i++) {
if(!arr[i]) arr[i]=null;
}
console.log(arr);
Output:
[ null, 2, null, null, null, null, null, 10 ]
null (including 0 and "" and NaN, etc.), not just undefined ones or holes.