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olizilla gets up close and functional with javascript. withCanvas provides a temporary canvas to another function, and always remembers to clean up after itself.
// Provide a function with a temporary canvas, encapsulating the creation and clean up code.
function withCanvas(/*canvas => Any*/ use) {
var b = document.body;
// create canvas
var canvas = document.createElement("canvas");
// canvas doesn't draw well unless it's added to the page
// do the user code
var result = use(canvas);
// clean up
// return anything there is to return
return result;
var video = document.getElementById('someVideo');
// usage, do something with a temporary canvas
var src = withCanvas( function(canvas){ // anonymous function, canvas => String
var ctx = canvas.getContext('2d');
ctx.drawImage(video, 0, 0, canvas.width, canvas.height);
return ctx.canvas.toDataURL('image/png');
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