why alert not working in Javascript

Question

i am designing a constructor function of an object type called Product that takes 3 parameters: aProdID, aDesc, and aPrice. displays the product object details by using alert(). For example, the output alert window should show the following if a product object is created with “A001”, “Coke”, “6” for the product number, product description, and product price respectively.

function product(aProdID, aDesc,aPrice){
     var quantity=0
     this.aProdID=aProdID;
     this.aDesc=aDesc;
     this.aPrice=aPrice;
     return aProdID, aDesc,aPrice;
}
var product1= new product('A001','Coke',6)

alert(product1);

But it display [Object Object] What's wrong with that? thanks a lot

You are alerting a JS object. You need to convert it to a string. alert(JSON.stringify(product1)); — Kalpesh Singh
– Kalpesh Singh, Commented Mar 5, 2017 at 10:02
If you're doing this for debugging purposes, use console.log() it shows much more information and allows you to track object references. In Chrome, you can activate the console with Ctrl + Shift + I. — dodov
– dodov, Commented Mar 5, 2017 at 10:07

Christos · Accepted Answer · 2017-03-05 10:15:40Z

3

The product1 is an object. When you call the alert passing product1 as a parameter, the the toString method of the product1 is called. Since you haven't overriden this method, you see the default output, which it [Object object].

function Product(aProdID, aDesc, aPrice){
     this.aProdID=aProdID;
     this.aDesc=aDesc;
     this.aPrice=aPrice;
}

Product.prototype.toString = function(){
    return 'ProductId: ' + this.aProdID + 'Desc: ' + this.aDesc + 'Price: '+ this.aPrice;
}

var product1= new Product('A001','Coke',6)

alert(product1);

Side notes

As you will notice I renamed he constructor function from product to Product. This is a very common convention in the JavaScript language, in order to notify the reader of you code that this function is a constructor function (one that can be used along with the new operator to create other objects).

Furthermore, I removed the return statement, since a constructor function should not have a return statement. Last but not least I deleted the local variable called quantity, since its not used anywhere.

Below you will find two very helpful links regarding this context:

edited Mar 5, 2017 at 10:15

answered Mar 5, 2017 at 10:02

Christos

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1 Comment

Wika Over a year ago

thanks a lot . Your explanations are very clear. since i fully understand what you mean even though i study js soon.Especially revise my basic concept

omar Samara · Accepted Answer · 2017-03-05 10:04:54Z

0

firstly you are using new to call the function and new always create object so the alert will be an object.

answered Mar 5, 2017 at 10:04

omar Samara

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Comments

Bc96 · Accepted Answer · 2017-03-05 10:05:30Z

0

Ohh same think happend to me then i found out that my information is be store in as object so in your case

alert(product1.aProdID);

To get the "A001"

answered Mar 5, 2017 at 10:05

Bc96

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