Javascript function scope when passing object as a parameter

Question

Hi I have the following javascript code

var skyrimCity = function(object) {
    object = {
      'world': 'whiterun'
    };
  },
  skyrim = function(object) {
    object.world = 'skyrim';
  },

  elderScrolls = {
    'world': 'tamriel'
  };
console.log(elderScrolls); // printed value ? -> {world: "tamriel"}

skyrimCity(elderScrolls);
console.log(elderScrolls); // printed value ? -> {world: "tamriel"}

skyrim(elderScrolls);
console.log(elderScrolls); // printed value ? -> {world: "skyrim"}

Inside skyrim function I changed the value of world but I can see it outside the function as well. I am wondering why the scope of this change propagated outside the function? Is passing an object inside a javascript function always passed as a reference to the original object itself?

Arrays, functions and objects are all passed by reference in JS, always. — Sebastien Daniel
– Sebastien Daniel, Commented Apr 25, 2016 at 20:25
"Is passing an object inside a javascript function always passed as a reference to the original object itself?" Yep, pretty much the same how it works in other popular languages as well (Java, PHP, Python). — Felix Kling
– Felix Kling, Commented Apr 25, 2016 at 20:27
to be pedantic, object are passed "byValue" in JS, it's just that the value is a ref to the object... — dandavis
– dandavis, Commented Apr 25, 2016 at 20:36

JLRishe · Accepted Answer · 2016-04-25 20:41:14Z

3

Is passing an object inside a javascript function always passed as a reference to the original object itself?

Yes, pretty much. In JavaScript, anything that's not a primitive type (number, boolean, string) is a reference type. If you pass an object into a function, you are passing a reference to the original object. If that object is modified inside a function, the original object is modified.

In other words, this has nothing to do with variable scope but rather with what the variables are actually referring to.

edited Apr 25, 2016 at 20:41

answered Apr 25, 2016 at 20:25

JLRishe

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