In JavaScript, typeof {} returns "object", while evaluating {} returns undefined. Why is this?
var a;
a; //undefined
{}; //undefined
typeof a === typeof {}; //false
Asked
Active
Viewed 106 times
-1
Michael Jasper
- 7,962
- 4
- 40
- 60
-
7Why would an empty object be undefined? Where did you come up with that! – adeneo Mar 17 '14 at 14:59
-
when you mean evaluating, are you meaning `eval()` – Amit Joki Mar 17 '14 at 15:01
-
@adeneo It is when it's considered an empty block :) – Ian Mar 17 '14 at 15:15
-
1@Ian - Indeed, just randomly typing `{}` does not an object make. – adeneo Mar 17 '14 at 15:18
1 Answers
5
That's because typeof a is "undefined" and typeof {} is "object":
console.log(typeof a); // "undefined"
console.log(typeof {}); // "object"
Also, as @adeneo commented, {} is not undefined:
console.log({} == undefined); // false
T.J. Crowder
- 1,031,962
- 187
- 1,923
- 1,875
Danilo Valente
- 11,270
- 8
- 53
- 67
-
2E.g., the question is based on a misconception: `{}` is not "undefined" in any sense of the word, and certainly not in the technical sense of having the type `"undefined"`. – T.J. Crowder Mar 17 '14 at 15:02