I guess I got used to it, I started geeking out and reading it since the 3rd edition. I don't think you can put this at the end of your constructor: If you return 5 you will get an empty object, and if you return an object then n will probably point to this object. es6 typescript @CMS so basically if you set some attributes on a, @George, yes, it's accurate. It's as easy as it said in documentation (new operator) : The object returned by the constructor function becomes the result of the whole new expression. To subscribe to this RSS feed, copy and paste this URL into your RSS reader. Show that involves a character cloning his colleagues and making them into videogame characters? There are actually many common OOP patterns in Javascript that do manually return an object in a constructor. limited resources or whatnot. Trying to simplify the existing answers by providing discrete examples proving that: Only constructors that return primitive or undefined implicitly create a new instance of themselves. But if the returned value is an object reference, that will be the returned value, e.g. US to Canada by car with an enhanced driver's license, no passport? n is an instance of SomeObject (call n.shout() to prove it), 1) If you return a primitive type, like a number or a string, it will be ignored. What about garbage collection? Otherwise the exact object returned by the constructor is used as is. rev2022.7.21.42639. What is the !! web.archive.org/web/20100216124827/http://www.gibdon.com/2008/, gibdon.com/2008/08/javascript-constructor-return-value.html, Design patterns for asynchronous API communication. I believe either one of these: @George, thanks for noticing!. By the Javascript spec, when a function is invoked with new, Javascript creates a new object, then sets the "constructor" property of that object to the function invoked, and finally assigns that object to the name this. a)The newly-instantiated object How do I return the response from an asynchronous call? This means that, if the constructor does not return undefined or primitive, we can have the following, which might feel weird to people coming from java: Using the same constructor, check in practice how the instance is different when undefined or primitive is returned: Additional note: Sometimes a function could act as a constructor even if it is not called as a constructor: You shouldn't return anything in a constructor. Connect and share knowledge within a single location that is structured and easy to search. What values can a constructor return to avoid returning this? Why is prototype undefined on return from constructor? The constructor returns the this object. Just note that for your point no. The article in the link above alludes to "managing it procedurally", but the article is now 10 years old. Is there a PRNG that visits every number exactly once, in a non-trivial bitspace, without repetition, without large memory usage, before it cycles? What function constructor returns in JavaScript, returning an object from a javascript function. How do I remove a property from a JavaScript object? language is quite technical and dry. If the constructor function doesn't explicitly return an object, the object created in step 1 is used instead. Is there any change to that in newer implementations of javascript classes? On the last version of the spec would be. Actually its a quiz question, what will be the answer? A constructor is used to initialize the object. Why do constructor functions return objects, but not primitives in JavaScript? Why does this constructor not return a string? Making statements based on opinion; back them up with references or personal experience. You can now choose to sort by Trending, which boosts votes that have happened recently, helping to surface more up-to-date answers. What is the most efficient way to deep clone an object in JavaScript? That's the object you have access with the this keyword inside the constructor when called with the new keyword. This would allow you to manage the Asking for help, clarification, or responding to other answers. What is the difference between call and apply? Laymen's description of "modals" to clients. Even Douglas Crockford is ok with it. How should I deal with coworkers not respecting my blocking off time in my calendar for work? How can I remove a specific item from an array? By clicking Accept all cookies, you agree Stack Exchange can store cookies on your device and disclose information in accordance with our Cookie Policy. To learn more, see our tips on writing great answers. 2) Otherwise, you will pass back the object. It either times out or redirects to a non programming page. You've come a long way coure2011. : If you are interested on the internals of the new operator, you can check the algorithm of the [[Construct]] internal operation, is the one responsible of creating the new object that inherits from the constructor's prototype, and to decide what to return: When the [[Construct]] internal method for a Function object F is called with a possibly empty list of arguments, the following steps are taken: The second piece of magic eluded to above is the ability for a Yes, the spec. How does a tailplane provide downforce if it has the same AoA as the main wing? n is an object instance of MyConstructor. MyConstroctor is great. What does "use strict" do in JavaScript, and what is the reasoning behind it? than a reference to a new instance. Consider the following constructor that returns exactly what we pass to it. Site design / logo 2022 Stack Exchange Inc; user contributions licensed under CC BY-SA. appoints fx d)Whatever is the return statement; the newly-instantiated object if no return statement. Find centralized, trusted content and collaborate around the technologies you use most. Trending is based off of the highest score sort and falls back to it if no posts are trending. cadiz need before 2021 @CMS the link appears to be broken. Why is the US residential model untouchable and unquestionable? What is returned from a custom object constructor? Thanks for contributing an answer to Stack Overflow! number of actual instances yourself if needed; possibly for reasons of Why had climate change not been proven beyond doubt for so long? Once the function body is executed, Javascript will return: ANY object if the type of the returned value is object: The this object if the function has no return statement OR if the function returns a value of a type other than object: Basically if your constructor returns a primitive value, such as a string, number, boolean, null or undefined, (or you don't return anything which is equivalent to returning undefined), a newly created object that inherits from the constructor's prototype will be returned. notepad awali memasukkan Nope, just tested on firefox, if i return 5 it gives me default object. (Normally constructors don't return a value, but they can choose to do so if they want to override the normal object creation process.). @George, you're welcome. constructor to return a specific, possibly pre-existing object, rather c)Whatever is the return statement You then have access to the this object from the body of the function. b)undefined - constructors do not return values Check the usages: The same rules as above apply also for class constructors. What is the JavaScript version of sleep()? If I return some value or object in constructor function, what will the var get? By clicking Post Your Answer, you agree to our terms of service, privacy policy and cookie policy. Functions and constructors are exactly the same in JavaScript, but how you call them changes their behaviour. Strange behaviour of Javascript `new` from `function`. Where developers & technologists share private knowledge with coworkers, Reach developers & technologists worldwide. 2, if you are on strict mode, on a "normal function call". In case you want to know what happens is that if you return 5 then n will simply be an empty object and if you return for example { a: 5 }, then n will have a property a=5. and if i return some object it gives me that object. How does one show this complex expression equals a natural number? Announcing the Stacks Editor Beta release! Never edit that. How do map designers subconsciously lead players? Javascript new operator *always* overrides return value? (not not) operator in JavaScript? If you have any questions, feel free to contact me through twitter or drop me a mail: [email protected] Cheers! Grep excluding line that ends in 0, but not 10, 100 etc. In Javascript, why does returning a function from a constructor function ruin the object?