View Full Version : Determine, the browser supports canvas (paperjs) or not
06-22-2012, 11:21 PM
Please tell, how can i determine, the browser supports canvas (paperjs), or not ?
06-23-2012, 12:07 AM
var canvas= document.createElement('canvas'),
06-23-2012, 12:23 AM
Thanks, but tell please, which means that two exclamation here:
06-23-2012, 04:31 AM
!! basically converts anything to a boolean. ! is the logical NOT operator, so it will convert a falsy value to true and a truthy value to false. Doing this two times in a row will make falsy values false and truthy values true.
I'd recommend using Modernizr's detection method, though, which is
var elem = document.createElement('canvas');
return !!(elem.getContext && elem.getContext('2d'));
I don't know enough about the cross-browser pitfalls of canvas to tell you which browser fails the other check, but if they are doing it this way, it can't be a bad idea.
(I don't quite get the reason for the canvas= null in that other snippet — it doesn't do anything.)
06-23-2012, 06:04 AM
I don't quite get the reason for the canvas= null
It does nothing in many browsers, but there are some browsers who's memory usage increases with every new html element created by a script, even those elements that are not added to the document tree. If you don't care about that, you can make a simpler test and call it just once-
06-23-2012, 01:38 PM
It does nothing in many browsers, but there are some browsers who's memory usage increases with every new html element created by a script, even those elements that are not added to the document tree.
Do you have some documentation on the behavior canvas= null is a workaround for? I can't quite imagine a situation where this would make a difference — the reference would be removed at the end of the function anyway, since converting to boolean prevents the forming of a closure, so I don't see how, after the function has run, there's any difference a browser bug could act upon.
Btw, the additional elem.getContext('2d') check seems to be necessary for some mobile devices.
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