Javascript multiple comparison expressions syntax

Question

By gut-feeling I know the following to be wrong syntax, or at least not working as intended (tried it), but there is no error thrown either:

var x = 2;
if (1 < x < 3) ...

I guess the VM evaluates part of the expression first, then compares it to the rest, but does anybody actually know (with documentation link, preferably) what exactly is going on here?

Edit: I found a similar question that has solutions of how to write this, but I am actually interested in what is happening behind the scenes here.

2 revs · Accepted Answer · 2014-07-10 08:59:58Z

2

Use this :

if (1 < x && x < 3)

What you were doing was

if (
    (1 < x) // boolean, cast to 0 or 1
    < 3
)

This page from the MDN on operator precedence explains that < is interpreted from left to right.

edited Jul 10, 2014 at 8:59

community wiki

2 revs
dystroy

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3 Comments

kontur Over a year ago

Thanks, I am not actually looking for a solution on how to write this, but for answers explaining what is happening (documentation for it).

Denys Séguret Over a year ago

@kontur Is my answer clear enough now ? What's missing ?

kontur Over a year ago

Why is 1 < x evaluated before x < 3, and why is this not invalid syntax? Or looking at the intuitively expected result, why does this not check if x is within the bounds of 1 and 3.

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