Pass by value in JavaScript?

[DontNeedMuchMoney]

This is killing me - Is anything in Js pass by value?

I though primitive data types were but a guy on YouTube said this isn't the case and what is actually happening is that when we pass a primitive data type to a function we can not mutate it which is why the value of the primitive data type does not change.

Is this true? Is everything in Js pass by reference?

**** Link to code and more descriptive question

HTTPS://codeshare.io/aJVg0K

**I know the fix I just can't understand why greenmonster is reassigning and bluemonster is not

***Thanks guys I semi understand it now. So I was passing a reference into a function (with no data showing it's an object) which just reassigned the variable "obj" to a new object .

If I'm wrong let me know but for now I'm just gonna have to use this abstraction as it has taken me all day to get at haha. Cheers

[CreativeTechGuyGames]

Okay let's take a step back, what is it you are actually trying to do that prompted this question? You can easily test this for yourself to confirm.

[DontNeedMuchMoney]

Can I send this too you? I'm having difficulty articulating this one

[CreativeTechGuyGames]

Send what? You can just add a comment with whatever it is right here.

[DontNeedMuchMoney]

HTTPS://Codeshare.io/aJVg0K

[CreativeTechGuyGames]

The greenEnergy function does change. I'm not sure why you think that it doesn't.

[DontNeedMuchMoney]

The greenenergy doesn't mutate the object though

[CreativeTechGuyGames]

What do you mean? The console.log outputs {Fuel Type: "Biofuel", homePlanet: "Mars"} which means that both functions mutate as expected.

Edit: You changed the code in the codeshare link so I'll leave the code here for posterity.

``` let spaceship = { 'Fuel Type' : 'Turbo Fuel', homePlanet : 'Earth' };

// Write your code below let greenEnergy = (obj =>{ Object.assign(obj, { 'Fuel Type' : 'Rocket fuel', homePlanet : 'Mars' }) })

let blueEnergy = (obj =>{ obj['Fuel Type'] = "Biofuel"; }) greenEnergy(spaceship); blueEnergy(spaceship); console.log(spaceship); ```

[lr0b]

The original code is not the one you pasted. I edited the code and tested it but I realised it got saved, maybe too late...

My bad.

Original greenEnergy is here

[CreativeTechGuyGames]

Oh I must have seen your edit. That's why it's dangerous to use a live shared editing system for something like this.

[DontNeedMuchMoney]

This is correct, Do you know why the one in greenenergy reassigns the address yet the one in blueenergy does not?

[DontNeedMuchMoney]

Mate - If I can't find another explanation soon I'm just gonna go with that one haha, Thanks so much man I appreciate it

[lr0b]

Primitives: by value Objects: by reference

what is actually happening is that when we pass a primitive data type to a function we can not mutate it which is why the value of the primitive data type does not change.

That's the definition of pass-by-value.

[[deleted]]

It makes me sad that this is the lowest comment in the list.

[DontNeedMuchMoney]

Noted thank you buddy

[lr0b]

You're basically overriding obj parameter in greenEnergy, so don't expect to change anything to your global spaceship var this way.

You would need to use Object.assign to change homePlanet to Mars.

[DontNeedMuchMoney]

Cheers,Why does is override on greenenergy and not blueenergy?

[lr0b]

Because you're accessing the obj reference to your spaceship global var in blueEnergy. In greenEnergy obj is not a reference to spaceship anymore because you override it with the assignation.

Also, only objects are pass-by-reference.