Read javascript file and execute code

Tag: javascript,html,html5,canvas

I'm building a map similar to Google Maps using HTML5 canvas. I'm also creating a tiling system where tiles are only loaded when dragged on screen.

So I have multiple javascript files that will draw on the canvas, each one a tile. One of the files might look like this (ctx being the canvas 2d context):

ctx.fillStyle="rgb(255,255,255)";
ctx.beginPath();
ctx.moveTo(256,197);
ctx.lineTo(177,241);
ctx.fill();

Now, I know one method of calling and executing the javascript files, which is like so:

function getTile(src){
      var tileScript = document.createElement('script');
      tileScript.src = src;
      var head = document.getElementsByTagName('head')[0];
      head.appendChild(tileScript); }

But I don't really want large numbers of script tags being added to the document head. With all the layers in the map, this might end up being a ridiculous number of scripts like 50.

Is there another method of reading and executing these files? Alternatively, if anyone could suggest an entirely better method of going about this, I would be open to suggestions.

Best How To :

If you just need the coordinates, use Ajax to read a .json File. Then you could execute the function above with your data.

JSON Example:

[[784,457],[759,989]] <- your coordinates

Ajax call:

function loadJSON() {
    var xmlhttp;

    if (window.XMLHttpRequest) {
        // code for IE7+, Firefox, Chrome, Opera, Safari
        xmlhttp = new XMLHttpRequest();
    } else {
        // code for IE6, IE5
        xmlhttp = new ActiveXObject("Microsoft.XMLHTTP");
    }

    xmlhttp.onreadystatechange = function() {
        if (xmlhttp.readyState == 4 && xmlhttp.status == 200) {
           render(xmlhttp.responseText)     //render your map with the response
        }
    }

    xmlhttp.open("GET", "your_json_file.json", true);
    xmlhttp.send();
}

The render() function:

function render(response){
   var json = JSON.parse(response); //parse the response to json
   ctx.fillStyle="rgb(255,255,255)";
   ctx.beginPath();
   ctx.moveTo(json[0][0],json[0][1]);
   ctx.lineTo(json[1][0],json[1][1]);
   ctx.fill();
}

Or if you realy just want to eval your functions, execute the eval() function on your Ajax Response:

eval(xmlhttp.responseText);

but remember that this is very uncertain!

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