I'm trying to loop through a sparse array and fill in sparse elements with a value.
['foo', 'bar', , , ,].map(el => el || 'default') // returns ["foo", "bar", undefined × 3]
How would I return ["foo", "bar", "default", "default", "default", "default"]
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";
}
}
default, but I don't think there's any way around that.
default.
default than element entries - perhaps that was a mistake?This should do it:
function Fill(n, _default) {
return Array.apply(null,n).map(function(val) {
return val || _default;
});
}
var newa = Fill(myarray, "default");
console.log(JSON.stringify(newa));
Shown working here:
var myarray = ['foo', , 'bar', , , , ];
function Fill(n, _default) {
return Array.apply(null, n).map(function(val) {
console.log("val:" + val);
return val || _default;
});
}
var newa = Fill(myarray, "default");
console.log(JSON.stringify(newa));
Array.apply( null, [, , ,]).map( i => typeof i ), should return [ "undefined", "undefined", "undefined" ].undefined sparse entries with explicit undefined entries, and then replaces any falsey value found.
undefined.
mapcalls a provided callback function once for each element in an array, in order, and constructs a new array from the results. callback is invoked only for indexes of the array which have assigned values; it is not invoked for indexes which have been deleted or which have never been assigned values."map()still has those positions.