new object as parameter in javascript

Question

I have simple one line function. Function received argument as an object and I am assigning a value to that object but it is alerting undefined. What is wrong with the code.

Fiddle

function custom(obj){
    obj.name="johnson";
}


var j= new custom(new Object());

alert(j.name)

Omri Aharon · Accepted Answer · 2014-11-29 12:28:13Z

4

That's because you're not returning the object:

function custom(obj){
    obj.name="johnson";
    return obj;
}

Fiddle

answered Nov 29, 2014 at 12:28

Omri Aharon

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2 Comments

Jitender Over a year ago

why we need to return obj. When we define function with this.name and use new operator then its work fine.

Omri Aharon Over a year ago

@amit Because var j= new custom(new Object());. The = there is expecting an object to be returned from the function. Otherwise, it returns nothing and j is assigned nothing.

Mihai Dinculescu · Accepted Answer · 2014-11-29 12:32:15Z

1

You have 2 errors in your code:
1. custom function should return obj;
2. there's no reason to have new custom in var j = new custom(new Object());

This is the working version of your code:

  function custom(obj) {
    obj.name = "johnson";
    return obj;
  }

  var j = custom(new Object());

  console.log(j.name)

answered Nov 29, 2014 at 12:32

Mihai Dinculescu

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