puzzling Uncaught TypeError: Object.keys called on non-object

Question

I have this code:

if(typeof x == 'object')
    return "{"+Object.keys(x)+"}";

It results in (Chrome):

Uncaught TypeError: Object.keys called on non-object

Can anybody tell me what's going on here? Btw: Firefox does the same.

ps: Don't know what the object is. Firefox debugging failed me.

Perhaps the answer is here: stackoverflow.com/questions/17319336/… — Robbert
– Robbert, Commented Sep 25, 2013 at 17:48
@JanDvorak: That's probably it. type null is "object", and would cause this exact error :) — gen_Eric
– gen_Eric, Commented Sep 25, 2013 at 17:50

SheetJS · Accepted Answer · 2013-09-25 17:50:58Z

7

x is most likely null (which is an object). You should explicitly check with if(typeof x === 'object' && x !== null)

Walking through the spec (to explain the logic):

If the Type(O) is not Object, throw a TypeError exception.

The table shows that the typeof null is in fact "object"

So in fact null satisfies typeof x === "object" and triggers a TypeError exception

answered Sep 25, 2013 at 17:50

SheetJS

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