Javascript - Loop through sparse array and replace sparse values

Question

I\'m trying to loop through a sparse array and fill in sparse elements with a value.

[\'foo\', \'bar\', , , ,].map(el => el || \'default\') // returns

Answer 1

Since .map (and also .forEach) will skip sparse values there's no option except to use a loop, but you should explicitly check for the absence of the missing keys

for (var i = 0, n = a.length; i < n; ++i) {
    if (!(i in a)) {       // explicit check for missing sparse value
        a[i] = "default";
    }
}