On 3/14/15, acmesquares . <acmesqua...@gmail.com> wrote: > It would be great if there was a promise-based version of toBlob. Same > parameters as toDataURL, but return a Promise to a blob. > I use toBlob heavily with other promise APIs, and this one really stands > out as in need of modernization. > Hi Adria,
toBlob: https://html.spec.whatwg.org/multipage/scripting.html#dom-canvas-toblob ... The disparity between toDataURL - sync - and toBlob - async - can be awkward to handle. How would you write it as a promise? I don't agree that a promise would make that better; IMO it would just move the place of the callback. Maybe you can offer more insight on it. You can use a callback in the enclosing scope for both, as an adapter for toBlob. For example, (I helped anonymously get this working): - https://github.com/coremob/camera/blob/master/vanilla/js/main.js#L339 function getBlobFromCanvas(canvas, data, callback) { if (canvas.toBlob) { //canvas.blob() supported. Store blob. // (GS) This assignment is still a mistake; should result `undefined` var blob = canvas.toBlob(function(blob){ data.photo = blob; callback(data); }, 'image/jpeg'); } else { // get Base64 dataurl from canvas, then convert it to Blob var dataUrl = canvas.toDataURL('image/jpeg'); data.photo = util.dataUrlToBlob(dataUrl); if(data.photo == null) { console.log('Storing DataURL instead.'); isBlobSupported = false; data.photo = canvas.toDataURL('image/jpeg'); } callback(data); } } A comment on comments: I generally initial my code review comments so that once all the issues have been resolved, the resultant code has as few explanatory comments as needed (deliberate omission of copyright notice is tantamount to professional fraud). This strategy leads to asking if there are any comments left, and helps motivate the removal of comments which leads to authoring code that is self-explanatory and well-named. It also avoids misleading comments, or situations where the code comments fall out of sync with what the code is actually doing, such as in the example above:- "//canvas.blob() supported. Store blob." This code comment review practice can be replaced by repo commit comments (stash/gitlab/github), but comments work great in email or other mediums such as this (despite contradicting articles http://www.thinkful.com/learn/javascript-best-practices-1/#Comment-as-Much-as-Needed-but-Not-More ) But to get back to your `toBlob` promise idea, would you want it as a new method like `getBlob(mimeType, quality)`? But then what about toDataURL? Would you have that as a promise, too, or would you leave it alone? canvas.getBlob(mimeType, quality).then(callback, errback); ~ vs ~ var dataUrl = canvas.getDataURL(mimeType, quality); util.dataUrlToBlob(dataUrl, callback, errback); ? -- Garrett @xkit ChordCycles.com garretts.github.io personx.tumblr.com