About Javascript For Loop

Question

what i want to do

if(data){
var loop = var i = 0; i < arr.length; i++; // ASC
} else { 
loop = var i = arr.length-1; i > -1; i--; // DSC
}
for(loop){ ..content.. }

How can I do something like this?

• mwilson: Are you just trying to sort data?
• Sebastian Simon: No. But you could use Array iteration methods like forEach, possibly using reverse.
• Nicolas: it's not efficient to do it that way, you would be better having two separate function with one loop in each.
• Juan: Possible duplicate of Sort array by firstname (alphabetically) in Javascript

Answer 1

If you're trying to sort the array, then check out .sort: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Array/sort

const arr = [4, 2, 5, 1, 3];
const data = true;
 
if (data) {
 arr.sort((a, b) => a - b); // asc
} else {
 arr.sort((a, b) => b - a); // desc
}
console.log(arr)

If you want to loop through the array from the end instead of start, then check out .reverse: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Array/reverse

const arr = [4, 2, 5, 1, 3];
const data = true;
 
if (data) {
 arr.reverse()
}
arr.forEach(item => {
 console.log(item)
})

In JavaScript you rarely use a standard for loop (though you can) and instead use iterators like .forEach, .reduce in combination with array functions like .reverse, .concat, etc.