Here are some dumb things to do with JavaScript’s Number prototype!

DISCLAIMER: Fooling around with any native object’s prototype is generally considered to be a bad idea. These examples are provided as demonstrations only, but they’re not recommended for use in “serious” code, or at least, any code you share with anybody.

Ain’t no time like Ruby #times

You can add a times method to JavaScript, just like Ruby’s #times method

(Note: you have to wrap the number in parentheses!)

(5).times(i => console.log(`I can count to ${i}!`));

But if Ruby’s not your thing, or you don’t want to deal with an awkward callback there’s another way to do the same thing, but with a for-loop:

for (let i of number)

This uses a few feature introduced in ECMAScript 2015: generators, and iterators (accessed with Symbol.iterator).

This allows for the following usage:

for (let i of 5) {

How is this different from the classical C-styled for-loop (e.g., for (var i = 0; i < MAX; i++))? In behaviour, it’s almost identical. The only difference is that modifying the “counter” variable (in this case, i), has no effect. The amount of repetitions stays the same (since the counting state is actually kept inside the generator). For example, the following will print “Hi!” 5 times:

var i;
for (i of 5) {
    i = 4;

You can still exit early using break, however:

for (let i of 5) {

As for performance, it’s up to the JavaScript engine (V8 or SpiderMonkey, or what-have-you) to optimize one approach over the other.

The for (let i of number) syntax is read with the same intent as the classical for-loop, but with a minimal amount of tokens. Less tokens, means less surface area for bugs and tiny, seemingly innocuous mistakes. For example, there is no keeping track of an explicit counter variable; this is entirely handled by the iterator. Mutating the “counter” has no effect, as demonstrated above (a feature, or annoyance, depending on your point of few). This new for-loop is attractive, as it gets straight to the point of what you’re trying to do: just do a thing n times!

Maybe we’ll get over the stigma of extending native prototypes—so long as we abide by the open/closed principle, our assumptions should not be violated. And it might even allow for cleaner, less error-prone code!