TypeOf Array is Gotcha!

For me one of the recent things was sort() method of the Array object:

[3,100,20].sort() //outputs [ 100, 20, 3 ]

I had no idea it sorts them as string literals.

I'm assuming that, once you realized the problem, you leveraged the Array object? That would be like:

const foo = {foo: 'bar'};
console.log(Array.isArray(foo));  // FALSE

It was precisely these kinda "gotchas" that led me to write my own little utility library that I now use all over my code. I wrote an article about it here:

dev.to/bytebodger/javascript-type-...

It gives me one central location where I can do Boolean checks as to whether a given variable meets a given condition.

For example, it uses this to determine whether something is an object:

const foo = [3,2,1];
console.log(is.anObject(foo));  // FALSE

And the logic it uses under the covers is:

typeof value === 'object' && !Array.isArray(value) && value !== null

Because, as you've pointed out, the typeof an array is... object. Also, typeof null is... object.

With a utility like this, you can also write more robust checks. For example, when you are writing a function that expects a string, you often don't want the parameter to be an empty string. That's why I have checks such for that too. I use it like this:

const foo = '';
console.log(is.aPopulatedString(foo));  // FALSE

The objectness is also very obvious in the fact that [] is truthy, unlike "" .