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Timeline for answer to What is the 'new' keyword in JavaScript? by Daniel Howard

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Feb 12, 2023 at 3:56 history edited Safwan Samsudeen CC BY-SA 4.0
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Dec 17, 2019 at 21:28 comment added Zac Taylor This lacks an explanation of what calling a constructor function without new does... If you're wondering what the answer is see below.
Jul 14, 2019 at 11:29 comment added Jose V This answer, in conjunction with this other answer to How does JavaScript .prototype work? really made it clear for me!
Dec 25, 2018 at 14:57 history edited DaveFar CC BY-SA 4.0
added missing word
Jan 4, 2018 at 22:19 history edited Jason Sears CC BY-SA 3.0
Removed comma splice
Feb 24, 2017 at 10:50 comment added Karan Kaw 2ality.com/2014/01/new-operator.html - This Explains it - No Fuss , No Confusion
Aug 7, 2016 at 9:08 history edited T.J. Crowder CC BY-SA 3.0
`null` isn't primitive, so change that wording slightly
Jul 9, 2016 at 5:49 history edited Dhruv Chadha CC BY-SA 3.0
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Jul 8, 2016 at 7:33 history edited Dhruv Chadha CC BY-SA 3.0
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Jul 8, 2016 at 7:26 history edited Dhruv Chadha CC BY-SA 3.0
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Jul 8, 2016 at 7:19 history edited Dhruv Chadha CC BY-SA 3.0
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May 9, 2016 at 6:53 comment added kernix Great explanation - missing only an example of what happens when returning a new object from the Construction function.
May 4, 2016 at 23:52 comment added wbyoung @masterxilo yes, the changes that I made on 3/6/14 are in line with what you're saying.
May 1, 2016 at 1:42 comment added masterxilo @wbyoung You misunderstood. It is not a copy, it is a reference to the same object Constructor.prototype is referencing. An assignment Constructor.prototype = {...} can make the constructor reference a different prototype object later on, to be used in subsequent constructions, but the object [[prototype]] referenced by the already created objects stays the same.
Nov 9, 2015 at 12:33 history edited Jonathan CC BY-SA 3.0
It is a common convention to Capitalize constructor functions in JS
Jan 10, 2015 at 2:51 history edited Josh Rieken CC BY-SA 3.0
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Jan 8, 2015 at 17:37 history edited user3310334 CC BY-SA 3.0
formatted code for cross-browser wrapping, and clarified a little
Jul 8, 2014 at 14:23 history edited Quentin CC BY-SA 3.0
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Jun 10, 2014 at 7:01 comment added Verron Knowles Oh my. In all my years of using javascript, I never knew this. Also the 'so java checks its prototype' is a live check. For example, if Test2 is constructed from Test1 beforehand, and Test1 adds a new function afterwards, Test2 still has access to that function. Simply amazing.
Jun 4, 2014 at 9:41 comment added rene @tomp I found a nice blog explaining the problem a little bit more.
May 21, 2014 at 10:11 comment added yuri Here another detailed explanation about creating new objects. It helps me understanding very well differences about object creation, the constructor property, prototype chaining: davidwalsh.name/javascript-objects-deconstruction
May 14, 2014 at 8:41 history edited sleske CC BY-SA 3.0
explain "constructor function"
Mar 6, 2014 at 19:47 history edited wbyoung CC BY-SA 3.0
Improved readability
Mar 6, 2014 at 19:42 comment added wbyoung I found the following information that explains how [[prototype]] or proto work here and updated the answer to reflect the fact that [[prototype]] is not actually copied. @silasdavis I'd love for you to review these changes.
Mar 6, 2014 at 19:40 history edited wbyoung CC BY-SA 3.0
Fixed inaccurate statements about copying (see https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object/proto)
Mar 6, 2014 at 19:17 comment added wbyoung @silasdavis is there an example that you can give that shows that [[prototype]] is a copy of Constructor.prototype at the time that new is used? Either I'm not understanding or something different is happening from what you're explaining.
Mar 6, 2014 at 18:57 history edited wbyoung CC BY-SA 3.0
Changed phrasing… "notice that" calls attention as if you're supposed to read it and it was originally important. "note" feels less compelling.
Mar 6, 2014 at 18:48 comment added wbyoung @tomp SubObjMaker.prototype = Object.create(ObjMaker.prototype); and you may need a shim for Object.create.
Feb 17, 2014 at 12:18 comment added Tom Pažourek There is a note that says Notice that this pattern is deprecated!. What is the correct up-to-date pattern to set the prototype of a class?
Jan 12, 2014 at 14:07 history edited Bergi CC BY-SA 3.0
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Dec 31, 2013 at 12:16 history edited Chai CC BY-SA 3.0
corrected spelling
Nov 30, 2013 at 10:26 history edited Alp CC BY-SA 3.0
edited body
Oct 23, 2013 at 15:18 review Suggested edits
Oct 23, 2013 at 15:31
Oct 10, 2013 at 18:07 history edited xdhmoore CC BY-SA 3.0
fixed grammar
Sep 30, 2013 at 20:20 review Suggested edits
Sep 30, 2013 at 20:26
Aug 27, 2013 at 23:59 history edited plalx CC BY-SA 3.0
Added missing information related to the return value
Aug 27, 2013 at 20:30 history edited Bolo CC BY-SA 3.0
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S Aug 8, 2013 at 9:44 history suggested Havvy CC BY-SA 3.0
Fixing inaccuracy on setting and getting internal [[prototype]] property.; Post Made Community Wiki
Aug 8, 2013 at 9:33 review Suggested edits
S Aug 8, 2013 at 9:44
Aug 4, 2013 at 11:40 comment added Robert Massaioli I ran a little JSFiddle test to see how the this object works in relation to the new keyword if anybody is interested: jsfiddle.net/yux2a/1
Jun 6, 2013 at 2:04 comment added charlie roberts a small point to add: a call to a constructor, when preceded by the new keyword, automatically returns the created object; there is no need to explicitly return it from within the constructor.
Apr 23, 2013 at 14:28 comment added Kamal Reddy @hvgotcodes you can get complete js internals here. ecma-international.org/publications/standards/Ecma-262.htm
Jan 15, 2013 at 4:45 history edited Igor CC BY-SA 3.0
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Oct 23, 2012 at 23:32 comment added Engineer @LonelyPixel ...And when using new, the meaning of this is modified to refer to the object just created via new -- exactly as when you create an object using brace-format (a la JSON) without new. So again, new can be completely circumvented. It has been stated elsewhere that new is actually a bit slower than creating an empty object. In any case, the future is Object.create(). I think it's fair to say that what you're already doing is probably similar to Crockford's explicit Object.create() from before it was added to the ES5 standard.
Oct 23, 2012 at 22:36 comment added Engineer @LonelyPixel new exists so that you don't have to write factory methods to construct/copy functions/objects. It means, "Copy this, making it just like its parent 'class'; do so efficiently and correctly; and store inheritance info that is accessible only to me, JS, internally". To do so, it modifies the otherwise inaccessible internal prototype of the new object to opaquely encapsulate the inherited members, mimicking classical OO inheritance chains (which aren't runtime modifiable). You can simulate this without new, but inheritance will be runtime modifiable. Good? Bad? Up to you.
Oct 23, 2012 at 21:25 comment added ygoe @NickWiggill He uses this, I don't.
Oct 23, 2012 at 17:14 comment added Engineer @LonelyPixel Maybe if you looked at JulianR's equally-excellent answer, below.
Oct 14, 2012 at 23:22 comment added sanz Doesn't the new keyword also set the 'constructor' property of the instance to the constructor function
Sep 24, 2012 at 21:09 comment added ygoe That's all good and interesting, but it doesn't answer an important part of the question. Especially, when the use of new is appropriate and when not. I can write a function that returns an object with functions, just like you can write a "class" definition. I can use methods of such an object when I use var obj = new func() as well as just var obj = func(), e.g. obj.method() works fine in both cases. It's the same to me right now. I don't use the this keyword though, I don't need it. Do I need new?
S May 30, 2012 at 19:51 history suggested corazza CC BY-SA 3.0
improved formatting
May 30, 2012 at 19:26 review Suggested edits
S May 30, 2012 at 19:51
S May 29, 2012 at 11:24 history suggested Silas Davis CC BY-SA 3.0
As George Mauer comment states when a new object is created from a base object the prototype must be copied to the new object not shared between itself and the base for the inheritance to work as expected.
May 29, 2012 at 10:53 comment added Silas Davis Perhaps that's not quite right.. An instance under prototype inheritance is exactly an object whose prototype contains the prototype of a base object; a might diverge from being an instance of A after being created var a = new A(), and var b = {} might converge into being an instance of A via b.__proto__ = A.prototype. In any case I don't think there is a chain of references maintained like in a class inheritance, it is all by virtue of the copying (and overwriting) of the prototype.
May 29, 2012 at 10:41 comment added Silas Davis George Mauer is right, only I think it is better to think of 'creating a new object from a base object' and 'copying the base object's prototype to the new object', than of creating a 'new instance', which is a concept that really belongs to class-based inheritance, not prototype-based inheritance. I have hopefully edited the question to reflect this...
May 29, 2012 at 10:39 review Suggested edits
S May 29, 2012 at 11:24
May 22, 2012 at 18:06 comment added Cemo Note that ObjMaker = function() {this.a = 'first';}; when you calling just ObjMaker(), you are assigning first to global object, usually window, but when you call new ObjMaker(), this is pointing current object so you can call new ObjMaker().a
S Mar 11, 2012 at 16:09 history suggested Anish Gupta CC BY-SA 3.0
improved formatting and improved grammar
Mar 11, 2012 at 15:20 review Suggested edits
S Mar 11, 2012 at 16:09
Feb 27, 2012 at 19:05 comment added Jim Blackler Question: what happens differently if ObjMaker is defined as a function that returns a value?
Feb 1, 2012 at 20:47 history edited Ufuk Hacıoğulları CC BY-SA 3.0
edited comments to make it more readable
Aug 31, 2011 at 22:14 comment added Art You can actually access the internal prototype object of the object via __ proto __ or this.constructor.prototype.
Jun 22, 2011 at 14:19 vote accept Alon Gubkin
May 11, 2011 at 0:39 comment added artur I think this is also explained in the classic MDC docs.
Apr 14, 2011 at 14:55 comment added Blub Just wanted to add: There is in fact a way to access the internal [[prototype]], by __proto__. This is however non-standard, and only supported by relatively new browsers (and not all of them). There is a standardized way coming up, namely Object.getPrototypeOf(obj), but it is Ecmascript3.1, and is itself only supported on new browers - again. It is generally recommended to not use that property though, stuff gets complicated real fast inside there.
Jan 10, 2011 at 20:56 comment added hvgotcodes @daniel, +1 for goodness. How did you find out what new does?
Sep 7, 2010 at 12:30 history answered Daniel Howard CC BY-SA 2.5
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