A neat little trick with JavaScript's indexOf()

Patrick Werner — Tue, 07 Aug 2018 12:31:54 +0000

Here's a little trick I picked up while browsing through some plugins I had to edit or extend again

var arr = [ 1, 2, 3, 'foo' ];

// old way
if (arr.indexOf('foo') > -1) {
    console.log('"foo" is in "arr"!');
}


// new way
if (~arr.indexOf('foo')) {
    console.log('"foo" is in "arr"!');
}

I wondered - how does that work? It's because of this little operator I never used or seen yet:

The Bitwise NOT-Operator `~`

It flips all bits of a number, I'm not sure how it exactly works but it seems that -1 is the only case of ending up with a falsy number, or rather a falsy expression: 0

So that means, we can take advantage of it and use it in indexOf (haven't seen any other uses yet though).

// you can also negate the statement, no separate parantheses needed
if (!~dailyRoutine.indexOf('☕️')) {
    console.log('Not a life worth living');
}

What do you think about this? I think it sure looks neat and saves up some characters in the code, but it could confuse people who read it afterwards (or look it up like me lol)

DEV Community: Patrick Werner

A neat little trick with JavaScript's indexOf()

The Bitwise NOT-Operator ~

The Bitwise NOT-Operator `~`