Why does (0 < 5 < 3) return true?

javascript compare operators boolean-logic
punkrockbuddyholly picture punkrockbuddyholly · Nov 3, 2010 · Viewed 11.9k times · Source

I was playing around in jsfiddle.net and I'm curious as to why this returns true?

if(0 < 5 < 3) {
    alert("True");
}

So does this:

if(0 < 5 < 2) {
    alert("True");
}

But this doesn't:

if(0 < 5 < 1) {
    alert("True");
}

Is this quirk ever useful?

Answer

Alan Geleynse picture Alan Geleynse · Nov 3, 2010

Order of operations causes (0 < 5 < 3) to be interpreted in javascript as ((0 < 5) < 3) which produces (true < 3) and true is counted as 1, causing it to return true.

This is also why (0 < 5 < 1) returns false, (0 < 5) returns true, which is interpreted as 1, resulting in (1 < 1).

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