Logo Questions Linux Laravel Mysql Ubuntu Git Menu
 

How to get class object's name as a string in Javascript?

Let's say I instantiate an object in Javascript like this:

var myObj = new someObject(); 

Now, is it possible to obtain the var object's name as string 'myObj' from within one of the class methods?


Additional details (edited):

The reason why I would like to get the name of the variable holding reference to the object is that my new myObj would create a new clickable DIV on the page that would need to call a function myObj.someFunction(). As I insert the new DIV I need to know the name of the variable holding reference to the object. Is there maybe a better way of doing this?


You are right, sorry for the mixup in terminology.

The reason why I would like to get the name of the variable holding reference to the object is that my new myObj would create a new clickable DIV on the page that would need to call a function myObj.someFunction(). As I insert the new DIV I need to know the name of the variable holding reference to the object. Is there maybe a better way of doing this?

like image 667
Miro Solanka Avatar asked Apr 25 '09 20:04

Miro Solanka


People also ask

How do I find the name of an object?

Access the name property on the object's constructor to get the class name of the object, e.g. obj.constructor.name . The constructor property returns a reference to the constructor function that created the instance object. Copied! We accessed the name property on the Object.

What is {} object in JavaScript?

This is the easiest way to create a JavaScript Object. Using an object literal, you both define and create an object in one statement. An object literal is a list of name:value pairs (like age:50) inside curly braces {}.

How do you find out what type an object is JavaScript?

Use the typeof operator to get the type of an object or variable in JavaScript. The typeof operator also returns the object type created with the "new" keyword. As you can see in the above example, the typeof operator returns different types for a literal string and a string object.


2 Answers

Shog9 is right that this doesn't make all that much sense to ask, since an object could be referred to by multiple variables. If you don't really care about that, and all you want is to find the name of one of the global variables that refers to that object, you could do the following hack:

function myClass() {    this.myName = function () {      // search through the global object for a name that resolves to this object     for (var name in this.global)        if (this.global[name] == this)          return name    }  } // store the global object, which can be referred to as this at the top level, in a // property on our prototype, so we can refer to it in our object's methods myClass.prototype.global = this // create a global variable referring to an object var myVar = new myClass() myVar.myName() // returns "myVar" 

Note that this is an ugly hack, and should not be used in production code. If there is more than one variable referring to an object, you can't tell which one you'll get. It will only search the global variables, so it won't work if a variable is local to a function. In general, if you need to name something, you should pass the name in to the constructor when you create it.

edit: To respond to your clarification, if you need to be able to refer to something from an event handler, you shouldn't be referring to it by name, but instead add a function that refers to the object directly. Here's a quick example that I whipped up that shows something similar, I think, to what you're trying to do:

function myConstructor () {   this.count = 0   this.clickme = function () {     this.count += 1     alert(this.count)   }    var newDiv = document.createElement("div")   var contents = document.createTextNode("Click me!")    // This is the crucial part. We don't construct an onclick handler by creating a   // string, but instead we pass in a function that does what we want. In order to   // refer to the object, we can't use this directly (since that will refer to the    // div when running event handler), but we create an anonymous function with an    // argument and pass this in as that argument.   newDiv.onclick = (function (obj) {      return function () {       obj.clickme()     }   })(this)    newDiv.appendChild(contents)   document.getElementById("frobnozzle").appendChild(newDiv)  } window.onload = function () {   var myVar = new myConstructor() } 
like image 64
Brian Campbell Avatar answered Sep 30 '22 21:09

Brian Campbell


Short answer: No. myObj isn't the name of the object, it's the name of a variable holding a reference to the object - you could have any number of other variables holding a reference to the same object.

Now, if it's your program, then you make the rules: if you want to say that any given object will only be referenced by one variable, ever, and diligently enforce that in your code, then just set a property on the object with the name of the variable.

That said, i doubt what you're asking for is actually what you really want. Maybe describe your problem in a bit more detail...?


Pedantry: JavaScript doesn't have classes. someObject is a constructor function. Given a reference to an object, you can obtain a reference to the function that created it using the constructor property.


In response to the additional details you've provided:

The answer you're looking for can be found here: JavaScript Callback Scope (and in response to numerous other questions on SO - it's a common point of confusion for those new to JS). You just need to wrap the call to the object member in a closure that preserves access to the context object.

like image 40
Shog9 Avatar answered Sep 30 '22 23:09

Shog9