Functional programming error

JavaScript
1 
var obj = {

  y: 4,

};

var nonMutatingFn = function (obj) {

  var newObj = {

    x: obj.y,

  };

  newObj.x += newObj.x + 1;

  return newObj;

};

nonMutatingFn();

//Can someone help out with what’s causing the error in this pls?

2

Well, for one thing, nonMutatingFn takes an obj as an argument but you are calling it without passing in an object.

3

So how do I call it? I’m not getting any output when I pass an object while calling the nonMutatingFn. @bbsmooth

4

var password = [1,2,3,4,5,6]
That is in the global scope i.e can be referenced anywhere.

Functions are exactly like maths’ functions. If you write an argument, that’s only a placeholder. Code:

let x = 5
var fn = function(){ 
return x
}
fn()

What will that return? Now…

let x = 5
var fn = function(x){ 
return x
}
fn()

What would that return?

When an argument has the same than a global variable, it overwrittes it. So function (x){//} is much like saying function (let x){//}

And yet x here is undefined, not assigned.

Now if you pass obj (or x) you’re redefining obj like this let obj; so it’s undefined inside the function.

I just wanted to remaind you of that…in case it helps…

Edits
Sorry I’ve tried to shorten the text as much as possible :slight_smile:

1 Like
5

Now if I understand the exercise, you want to return a new object with an updated value.

So I’d go about more or less like this:

let game = {score:20}

var updater= function(){
var newScore = {score: game.score}
newScore.score += newScore.score + 1
return newScore
}

let newObject = updater()
1 Like
6

I would probably not use a function that depends on a global variable like that.

1 Like
7

Well I kept it as close to the post as I could…I guess you can build on the top. I don’t mind…

8

You pass in the object to the function just like you would pass in any other value to a function. You defined nonMutatingFn as:

var nonMutatingFn = function (obj) { ... }

The anonymous function you are using to define nonMutatingFn takes one argument (obj). So when you call nonMutatingFn you must also pass in one argument.

1 Like