What is wrong with this code as I am not getting the desired output?

Question

<!DOCTYPE html>
<html>
<head>
<title>A generalized object declaration - Javascript</title>
</head>
<body>
<script type="text/javascript">
function myBooks(name,author,bookType,printCost,purchaseCost){
    this.name = name;
    this.author = author;
    this.bookType  =bookType;
    this.printCost = printCost;
    this.purchaseCost  =purchaseCost;
    var checkProfit = (function(){
        return this.printCost-this.purchaseCost;

    }());
}

var book1 = new myBooks('Elon Musk','Ashlee Vance','Biography',699,500);
document.write('Profit from '+ book1.name + ' = ' + book1.checkProfit);
</script>
</body>
</html>

Hi, I have written a basic code in Javascript in which I am declaring an object using constructor function. Here, in 20th line of my code, book1.checkProfit is getting value NaN while other variables are working fine. Can anyone explain the error in my code.

Why you are not use : `var checkProfit = this.printCost - this.purchaseCost` ? — MHS, Jul 11 '16 at 07:50
I am trying to learn and apply the concept of immediately invoked anonymous function. Therefor, preferring this way. — enthu_learner, Jul 11 '16 at 07:55
`checkProfit` is a local variable in `myBooks`, you can't access it from outside of the function. Define it as a property, i.e. `this.checkProfit = ...`. — Teemu, Jul 11 '16 at 07:59
Okay. But even if I am using this.checkProfit, it is still returning NaN. — enthu_learner, Jul 11 '16 at 08:05
the last parentheses is on wrong place it should be `(function() {}) ()` instead of `(function{}())` — webdeb, Jul 11 '16 at 08:10
I dont think so as I have previously used it the same way and have achieved output. — enthu_learner, Jul 11 '16 at 08:24

Piyush.kapoor · Accepted Answer · 2016-07-11T08:00:06.403

2

Use that = this , this inside your checkProfit is window

function myBooks(name,author,bookType,printCost,purchaseCost){
    this.name = name;
    this.author = author;
    this.bookType  =bookType;
    this.printCost = printCost;
    this.purchaseCost  =purchaseCost;
    var that = this;
    this.checkProfit = (function(){
        return that .printCost-that.purchaseCost;

    }());
}

OR you can use bind

function myBooks(name,author,bookType,printCost,purchaseCost){
    this.name = name;
    this.author = author;
    this.bookType  =bookType;
    this.printCost = printCost;
    this.purchaseCost  =purchaseCost;
    var that = this;
    this.checkProfit = (function(){
        return that .printCost-that.purchaseCost;

    }.bind(this)());
}

edited Jul 11 '16 at 08:00

answered Jul 11 '16 at 07:48

Piyush.kapoor

6,041
1
17
18

Tried this. Its not working for me. – enthu_learner Jul 11 '16 at 07:57
use this.checkProfit , you are tying to access the local variable of the function instance from outside – Piyush.kapoor Jul 11 '16 at 08:00
Rectified. Still not working. – enthu_learner Jul 11 '16 at 08:22
1

@AkshitaBhatt You're doing something wrong. Piyush.kapoor's answer [works as it is](https://jsfiddle.net/39q6hufq/) (replaced `.write` with `.body.innerHTML`, since jsFiddle doesn't accept `.write`). – Teemu Jul 11 '16 at 08:39
Thanks for the correct code, but still I am not able to understand the error in my code. Can anyone please explain? – enthu_learner Jul 11 '16 at 09:24

score 0 · Answer 2 · answered Jul 11 '16 at 08:27

Well this one worked out for me. Have a look!

function myBooks(name,author,bookType,printCost,purchaseCost){
    this.name = name;
    this.author = author;
    this.bookType  =bookType;
    this.printCost = printCost;
    this.purchaseCost  =purchaseCost;
    var that =this;
    this.checkProfit = (function(){
        return parseInt(that.printCost)-parseInt(that.purchaseCost);
    }.bind(this)());
}

What is wrong with this code as I am not getting the desired output?

2 Answers2