CODEWITHSUNDEEP
javascriptjqueryjavascript-objects
Andrei Oniga
Andrei Oniga

Reputation: 8559

JavaScript method that preloads image before displaying it doesn't work

Within an object constructor there's a method named addToViewport(), which has the role of simply displaying an image after preloading it:

window.onload = function(){

            function ViewportObject(){
                this.src = "https://chart.googleapis.com/chart?cht=qr&chs=500x500&chl=asdasdasd&choe=UTF-8&chld=L|0";
                this.addToViewport = function(){
                    // Determine the DOM object type to create
                        var DOM_elem = "img",
                            obj = $(document.createElement(DOM_elem)),
                            img = new Object();

                            obj.addClass("object");
                            obj.css({"z-index":"100","width":"300px","height":"auto"});

                            // Preload the image before rendering it and computing its size
                            img.src = this.src;
                            img.onload = function(){

                                obj.attr("src",this.src);
                                obj.appendTo("body");
                            }                       

                }
            }

            var o = new ViewportObject();   
            o.addToViewport();
        }

The problem I've come across is that the script doesn't enter the "onload" event handler block, so the image doesn't get displayed. I put together a web page with the same script as above on http://picselbocs.com/test/ for you to check out live.

What is it that I'm doing wrong here?

Upvotes: 0

Views: 4396

Answers (1)

Fresheyeball
Fresheyeball

Reputation: 30015

Try this:

change this

img = new Object();
....
img.src = this.src;
img.onload = function(){

    obj.attr("src",this.src);
    obj.appendTo("body");
}

to

img = new Image();
....
img.onload = function(){

    obj.attr("src",this.src);
    obj.appendTo("body");
} 
img.src = this.src;

Upvotes: 3

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