3

I am learning JavaScript and read that functions are like objects and can have properties set like this:

var person = function(){
}
person.name="John Smith"; //output ""
person.age=21; //output 21
person.profession="Web Developer"; //output "Web Developer"

Why is the name property blank?

Thanks

Andy
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    Long story short, it's [one of those quirky things](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Function/name) you will find in JS. – Brian Sep 19 '13 at 20:36
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    I'm amazed that there are so many answers saying you can't do this. It's definitely possible - see my answer: http://stackoverflow.com/a/41735602/993683 –  Jan 19 '17 at 06:53

6 Answers6

9

Because name is a non-standard, non-writable property of function objects. Function declarations and named function expressions are named, while you have an anonymous function expression whose name is "".

You probably wanted a plain object:

var person = {
    name: "John Smith",
    age: 21,
    profession: "Web Developer"
};
Bergi
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  • Thanks, I know about object literals but needed to understand why I couldn't set a function's name property – Andy Sep 19 '13 at 20:43
5

name is a special property because it gives the name of the function when defined like this:

function abc(){

}

In this case name would return the string "abc". This name cannot be changed. In your case, the function does not have a name, hence the empty string.

http://jsfiddle.net/8xM7G/1/

James Montagne
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2

You can change the name property!

The Function.name property is configurable as detailed on MDN.

Since it's configurable, we can alter its writable property so it can be changed. We need to use defineProperty to do this:

var fn = function(){};
Object.defineProperty(fn, "name", {writable:true});
// now you can treat it like a normal property:
fn.name = "hello";
console.log(fn.name); // outputs "hello"
0

You may want to use Prototype (see How does JavaScript .prototype work?) or simply turn the 'person' into a hash like so:

var person = {};
person.name="John Smith"; //output "John Smith"
person.age=21; //output 21
person.profession="Web Developer"; //output "Web Developer"
Community
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Tristan Cebulla
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0

You can use Object.defineProperty to change the value of the property (even without touching its writeable flag):

function fn () {}
console.log(fn.name) // Outputs fn

Object.defineProperty(fn, 'name', { value: 'newName' })

console.log(fn.name) // Outputs newName
CherryDT
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-1

The name property is set by the Function constructor and cannot be overwritten directly. If the function is declared anonymous, it will be set to an empty string.

For example:

var test = function test() {};
alert(test.name); // Displays "test"
test.name = "test2";
alert(test.name); // Still displays "test"
nullability
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  • Actually, `name`, `length` and `prototype` are not inherited but own properties of a function object. Gonna fix MDN :-) – Bergi Sep 19 '13 at 20:44