What is the difference between for loop and forEach?

Both are used to iterate over arrays, but they differ in performance, flexibility, and purpose.

The for loop is a core JavaScript statement that gives you full control over iteration:

      const arr = [1, 2, 3];
      for (let i = 0; i < arr.length; i++) {
        console.log(arr[i]);
      }
      

The forEach is an array method introduced in ES5 that accepts a callback and calls it for each element:

      const arr = [1, 2, 3];
      arr.forEach((num) => console.log(num));
      

Why is for loop faster?

forEach has two sources of overhead on every iteration: first, it
invokes your callback using .call() (a function call has a cost).
Second, it checks for empty slots in the array (i in this) on every
single iteration even when the array has no empty slots at all. The
for loop does neither of these things, and JavaScript engines like
V8 are highly optimized for its simple counter pattern.

Why was forEach created?

For readability. The classic for (let i = 0; i < arr.length; i++)
is noisy you have to declare a counter, write a condition, and
increment manually, just to access each element. forEach hides all
of that mechanics and lets you focus on the element itself. Arrow
functions later made it even cleaner. However, they also made its
optional thisArg parameter (used to set this inside the callback)
mostly obsolete, since arrow functions inherit this automatically.

When to use which:

      // Use forEach — simple iterations where readability matters
      arr.forEach((num) => console.log(num));

      // Use for loop — when you need break, continue, or max performance
      for (let i = 0; i < arr.length; i++) {
        if (arr[i] === target) break; // impossible with forEach
      }
      

Note: The for loop is strictly more powerful anything forEach does, for loop can do too, but not the other way around.