Javascript array non undefined element count
Solution 1:
You could use Array#forEach, which skips sparse elements.
let array = new Array(99999),
count = 0;
array[30] = undefined;
array.forEach(_ => count++);
console.log(count);The same with Array#reduce
let array = new Array(99999),
count = 0;
array[30] = undefined;
count = array.reduce(c => c + 1, 0);
console.log(count);For filtering non sparse/dense elements, you could use a callback which returns for every element true.
Maybe this link helps a bit to understand the mechanic of a sparse array: JavaScript: sparse arrays vs. dense arrays.
let array = new Array(99999),
nonsparsed;
array[30] = undefined;
nonsparsed = array.filter(_ => true);
console.log(nonsparsed);
console.log(nonsparsed.length);Solution 2:
The fastest & simplest way to filter items in an array is to... well... use the .filter() function, to filter out only the elements that are valid (non undefined in your case), and then check the .length of the result...
function isValid(value) {
return value != undefined;
}
var arr = [12, undefined, "blabla", ,true, 44];
var filtered = arr.filter(isValid);
console.log(filtered); // [12, "blabla", true, 44]