Javascript images loading function hangs up my browser

I'm trying to make simple game in Javascript and HTML so I need images function to load sprites. I'd like it to wait until image is loaded and then proceed to another image. Unfortunatly code I wrote stops my browser from working. I think that it's endless while loop that should be finished.

Here's my code:

var Sprites = {};
function NewSprite( Name, URL )
{
    Sprites[ Name ] = new Image( );
    Sprites[ Name ].Ready = false;
    Sprites[ Name ].onload = function ( )
    {
        this.Ready = true;
    }
    Sprites[ Name ].src = URL;

    while ( Sprites[ Name ].Ready === false );
}

When I run it without while loop at the end and check Sprites[ Name ].Ready value it gives me true so I think it should work.

I'm calling my function like this:

NewSprite( "img", "http://ift.tt/1D2GxhK" );

Thanks for help!