Dealing with Recursion on Large Inputs in JavaScript

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Ever tried to climb a ladder that stretches up to the moon? Me neither, but I imagine it would feel similar to dealing with recursion on large inputs in JavaScript. It's a seemingly insurmountable task, with the risk of toppling over (or in JavaScript terms, a stack overflow). But fear not! With the right tools and techniques, we can safely navigate this challenge. So get your space helmet on, and let's dive in!

Recursion and The Call Stack

First, let's understand how recursion works in JavaScript. Recursion is a technique in which a function calls itself to solve a problem. It's like a Russian doll: a bigger problem contains smaller versions of the same problem within it.

In JavaScript, each recursive call adds a new frame to the call stack. This is a pile of function calls that the JavaScript engine needs to keep track of. It's like a stack of pancakes: the most recent pancake (function call) gets added to the top, and gets eaten (executed) first.

function countDownFrom(n) {
    if (n > 0) {
        console.log(n);
        return countDownFrom(n - 1);
    }
    return n;
}

countDownFrom(5); // outputs 5, 4, 3, 2, 1

But what happens when we try to eat too many pancakes (recursive calls)? That's right, we get a stomachache (stack overflow).

Stack Overflow and Large Inputs

A stack overflow occurs when there are too many function calls on the call stack. The JavaScript engine has a limited amount of memory to store these function calls, so if your recursive function has a large input, it can quickly fill up the call stack and cause an error.

countDownFrom(100000); // Uncaught RangeError: Maximum call stack size exceeded

Tail Call Optimization

Luckily, there's a technique to handle recursion with large inputs: tail call optimization. Here's the gist: if the last action of a function is to call itself, the JavaScript engine can clear the current stack frame before making the recursive call. This means the call stack won't grow with each recursive call.

This sounds like a magic trick, right? But there's a catch: JavaScript does not fully support tail call optimization. However, you can enable strict mode to use it.

"use strict";

function countDownFrom(n, acc = 0) {
    if (n <= 0) {
        return acc;
    }
    return countDownFrom(n - 1, acc + n);
}

countDownFrom(100000); // no stack overflow error

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