CODEWITHSUNDEEP
javascriptobjectscopeparameter-passing
rameshsyn
rameshsyn

Reputation: 98

how to update value of property of an object through argument variable

I would like to increment property SCountDown of an object pomodoro with method customization, which has an argument chooseSession and this method is called within sessionPlus method passing SCountDown as an argument. when i call sessionPlus method , SCountDown property increments for once and when it is called for second time and so on , It doesn't increment.

Here's my code:

pomodoro = {   
 SCountDown: 0,
 customization: function(chooseSession) {
    chooseSession++;
     console.log(chooseSession);       
 },
 sessionPlus : function() {
    this.customization(this.SCountDown);        
 }
}
pomodoro.sessionPlus(); // it returns 1 , this is what i needed but
pomodoro.sessionPlus(); // it also returns 1, but what i need is 2.

Upvotes: 3

Views: 549

Answers (4)

Jswq
Jswq

Reputation: 776

pomodoro = {   
 SCountDown: 0,
 customization: function() {
 
     console.log(this.SCountDown);       
 },
 sessionPlus : function() {
    this.SCountDown=this.SCountDown+1;
    this.customization();        
 }
}
pomodoro.sessionPlus(); // it returns 1 , this is what i needed but
pomodoro.sessionPlus(); // it also returns 1, but what i need is 2.
May this help

Upvotes: 1

Monica Olejniczak
Monica Olejniczak

Reputation: 1156

JavaScript uses pass by sharing and since SCountDown is a primitive value (integer) it cannot be referenced in the way you are attempting to. It's always going to log as 1 because you will always be passing in the primitive value 0 and then incrementing that. You need to reference this.SCountDown directly instead of chooseSession.

var pomodoro = {
    SCountDown: 0,
    customization: function(chooseSession) {
        console.log(chooseSession);
    },
    sessionPlus: function() {
        this.SCountDown++;
        this.customization(this.SCountDown);
    }
}

pomodoro.sessionPlus();
pomodoro.sessionPlus();

Upvotes: 2

Yeldar Kurmangaliyev
Yeldar Kurmangaliyev

Reputation: 34234

When you pass this.SCountDown to customization, you pass its value (which is zero). Then, this value is incremented by 1 and it is outputed. The actual value of this.SCountDown never changes.

JavaScript passes primitives by value.
It means that there is no way to modify the primitive by passing it to a function.

function modify(a)
{
    a = a * 2;
}

var x = 2;
modify(x);
console.log(x); // 2

However, you can modify the inner properties of passed objects since JS uses call-by-sharing strategy.
Therefore, you can do the following:

function modify(o)
{
    o.val = o.val * 2;
}

var x = { val: 2 };
modify(x);
console.log(x.val); // 4

Upvotes: 1

balachandar
balachandar

Reputation: 825

Try this code. You need increment this.SCountDown not chooseSession

 pomodoro = {
   SCountDown: 0,
   customization: function(chooseSession) {
     console.log(chooseSession);
   },
   sessionPlus: function() {
     this.SCountDown++;
     this.customization(this.SCountDown);
   }
 }
 pomodoro.sessionPlus();
 pomodoro.sessionPlus();

Hope this will help you.

Upvotes: 1

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