Question

How can I build a loop in JavaScript?

Answer 1

For loops

for (i = startValue; i <= endValue; i++) {     // Before the loop: i is set to startValue     // After each iteration of the loop: i++ is executed     // The loop continues as long as i <= endValue is true } 

For…in loops

for (i in things) {     // If things is an array, i will usually contain the array keys *not advised*     // If things is an object, i will contain the member names     // Either way, access values using: things[i] } 

It is bad practice to use for...in loops to itterate over arrays. It goes against the ECMA 262 standard and can cause problems when non-standard attributes or methods are added to the Array object, e.g. by Prototype. (Thanks to Chase Seibert for pointing this out in the comments)

While loops

while (myCondition) {     // The loop will continue until myCondition is false }