JavaScript How to change parameter inside function?

Question

This is my code:

function makeCounter(x) {
    x = x || 0;
    var obj = {
        value: x,
        increment: function(){
            x = x + 1;
            return x;
        },
        decrement: function() {
            x = x - 1;
            return x;
        }
    }
    return obj;
} 
var counter = makeCounter();

console.log(counter.increment()); // output is 1
console.log(counter.value); // output is 0

Now, I want to know how to edit the code so that the value will be 1 after counter.increment().

Илья Зелень · Accepted Answer · 2018-08-16 03:44:15Z

6

You need to update value after the increase or decrease and use this.value instead of x variable.

function makeCounter(value = 0) {
    return {
        value,
        increment () {
            return ++this.value;
        },
        decrement () {
            return --this.value;
        }
    };
} 

let counter = makeCounter();

console.log(counter.increment()); // output is 1
console.log(counter.value); // output is 1

edited Aug 16, 2018 at 3:44

answered Aug 12, 2018 at 5:20

Илья Зелень

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2 Comments

connexo Over a year ago

Good solution, but this needs explanation, too.

Deadweight Over a year ago

Its nothing different then the other. He just shortened it. He is returning the object

brk · Accepted Answer · 2018-08-12 05:21:11Z

1

Update value using this.value & assign value of x to it

function makeCounter(x) {
  x = x || 0;
  var obj = {
    value: x,
    increment: function() {
      x = x + 1;
      this.value = x
      return x;
    },
    decrement: function() {
      x = x - 1;
      this.value = x
      return x;
    }
  }
  return obj;
}
var counter = makeCounter();

console.log(counter.increment()); // output is 1
console.log(counter.value); // output is 1

answered Aug 12, 2018 at 5:21

brk

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Comments

Tu Tran · Accepted Answer · 2018-08-12 05:23:58Z

1

You need to update value after the increase or decrease and use this.value instead of x variable.

You can see my code:

function makeCounter(x) {
    x = x || 0;
    return  {
        value: x,
        increment: function(){
            this.value = this.value + 1;
            return this.value;
        },
        decrement: function() {
            this.value = this.value - 1;
            return this.value;
        }
    }
}
var counter = makeCounter();

console.log(counter.increment()); // output is 1
console.log(counter.value); // output is 1
console.log(counter.increment())//output is 2
console.log(counter.value); // output is 2

answered Aug 12, 2018 at 5:23

Tu Tran

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Comments

vinay mavi · Accepted Answer · 2018-08-12 05:31:19Z

1

function makeCounter(x) {
    return {
        value: x || 0,
        increment () {
           // https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Operators/Arithmetic_Operators#Increment_() 
            return ++this.value;
        },
        decrement () {
           // https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Operators/Arithmetic_Operators#Decrement_(--) 
            return --this.value;
        }
    };
} 

let counter = makeCounter();

console.log(counter.increment()); // output is 1
console.log(counter.value);

answered Aug 12, 2018 at 5:31

vinay mavi

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Comments

andylamax · Accepted Answer · 2018-08-12 05:33:57Z

1

In case of nesting, you might fail to use this at some point, you can go with the object's name. as long as you are calling it inside a function

function makeCounter(x) {
    x = x || 0;
    var obj = {
        value: x,
        increment: function(){
            obj.value = obj.value + 1;
            return obj.value;
        },
        decrement: function() {
            obj.value = obj.value - 1;
            return obj.value;
        }
    }
    return obj;
} 
var counter = makeCounter();

console.log(counter.increment()); // output is 1
console.log(counter.value); // output is 1

answered Aug 12, 2018 at 5:33

andylamax

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Comments

maazadeeb · Accepted Answer · 2018-08-12 05:41:08Z

1

You could use a getter on the object being returned. You get control to do any business logic you like when you do counter.value.

You could change your code like so

function makeCounter(x) {
  x = x || 0;
  var obj = {
    get value() { return x; }, // Only change required
    increment: function() {
      x = x + 1;
      return x;
    },
    decrement: function() {
      x = x - 1;
      return x;
    }
  }
  return obj;
}
var counter = makeCounter();

console.log(counter.increment()); // output is 1
console.log(counter.value); // output is 1

answered Aug 12, 2018 at 5:41

maazadeeb

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