Javascript IN operator compatibility

Question

Can someone tell me since which ECMA version the IN operator is available and which browsers (versions) support it ?

Explanation:

The IN-operator can be used like the following:

var myObject = {
    Firstname: 'Foo',
    Lastname: 'Bar'
};

if('Lastname' in myObject){
    // Lastname is an attribute of myObject
}

Andy E · Accepted Answer · 2015-01-17 15:24:05Z

56

It is defined in ECMAScript 3rd edition. It is available in IE 5.5+ and all in-use versions of Firefox, Chrome, Opera and Safari.

You can use it safe in the knowledge that it will work.

You should err on the side of caution when using it to check event support. All implementations except older Firefox versions support "eventname" in element as a test for DOM events.

"onclick" in document.body; // -> false in old Fx, true in others
document.body.setAttribute("onclick", "");
typeof(document.body.onclick == "function"); // -> true in Fx

edited Jan 17, 2015 at 15:24

answered May 27, 2010 at 11:57

Andy E

346k86 gold badges482 silver badges452 bronze badges

Sign up to request clarification or add additional context in comments.

7 Comments

bobince Over a year ago

It's only in IE 5.5+; IE 5.0 was the ‘problem browser’ for in, though obviously that worry is long gone now.

Alex K. Over a year ago

FWIW I couldn't see it in the 2nd ed @ ecma-international.org/publications/standards/Ecma-262-arch.htm

bobince Over a year ago

@Nick: it certainly is in 3.0, even though IE didn't support it at the time of publication. ECMAScript 3.1 was the development name for what became the Fifth Edition.

Nick Craver Over a year ago

@bobince - You're indeed right, I had the 2nd edition, not the 3rd up when comparing and couldn't find section 11.8.7, it is in 3.0.

bobince Over a year ago

@Andy: you're right, that doc is indeed nonsense! I've got IE5/Win98 here and in definitely doesn't work.

|

Skilldrick · Accepted Answer · 2010-05-27 11:55:57Z

2

According to MDC, it's implemented in JavaScript 1.4.

According to Wikipedia:

Netscape Navigator 6.0
Firefox 1.0+
IE 5.5+
Opera 6.0+
Safari 3.0+
Chrome 1.0+

So I think you're probably OK :)

edited May 27, 2010 at 11:55

answered May 27, 2010 at 11:49

Skilldrick

71.1k37 gold badges182 silver badges231 bronze badges

4 Comments

Eric Over a year ago

because I can do undefined = 'defined!'; earlier in the code, which is obviously beneficial.

Eric Over a year ago

Really, you should have put that as another answer, as now our comments make no sense.

Adri w Ukraine Over a year ago

@Skilldrick you can strikeout text in an answer using the <s> tag apparently meta.stackexchange.com/questions/63768/…

Adri w Ukraine Over a year ago

note: I doubt Wikipedia is a reliable source regarding Javascript features browser versions support.

Collectives™ on Stack Overflow

Javascript IN operator compatibility

2 Answers 2

7 Comments

4 Comments

Your Answer

Linked

Hot Network Questions

Collectives™ on Stack Overflow

2 Answers 2

7 Comments

4 Comments

Your Answer

Sign up or log in

Post as a guest

Linked

Related