javascript: strict mode and objects

Question

I had some code that constructed an object:

function gridObjConst(id, itemName, itemPrice, itemListPrice, width, height, imgName) {

    this.id = id;
    this.itemName = itemName;
    this.itemPrice = itemPrice;
    this.itemListPrice = itemListPrice;
    this.width = width; 
    this.height = height; 
    this.imgName = imgName;

    return this;
}

I used the w3schools page as a guide: http://www.w3schools.com/js/js_objects.asp

It all worked fine. Then I added "use strict" to the top of my code and this function broke. Firebug reported: this is undefined - this.id = id

How do I fix this?

Answer 1

That means you are calling your constructor function without the new operator. You need to do this:

var myGridObjConst = new gridObjConst();

When you call the function without the new operator, this refers to the Window, but in strict mode it does not , hence your error.

Also note that you don't need to return this; from a constructor function. this will be returned automatically.

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As noted by @JoachimSauer, you should look at using MDN instead of W3Schools when learning JavaScript. The fact that prototypes are not mentioned anywhere on that page you linked to is absolutely ridiculous.