Convert base64 png data to javascript file objects

Question

I have two base64 encoded in PNG, and I need to compare them using Resemble.JS

I think that the best way to do it is to convert the PNG's into file objects using fileReader. How can I do it?

Answer 1

Way 1: only works for dataURL, not for other types of url.

function dataURLtoFile(dataurl, filename) {     var arr = dataurl.split(','), mime = arr[0].match(/:(.*?);/)[1],         bstr = atob(arr[1]), n = bstr.length, u8arr = new Uint8Array(n);     while(n--){         u8arr[n] = bstr.charCodeAt(n);     }     return new File([u8arr], filename, {type:mime}); }  //Usage example: var file = dataURLtoFile('data:image/png;base64,......', 'a.png'); console.log(file); 

Way 2: works for any type of url, (http url, dataURL, blobURL, etc...)

//return a promise that resolves with a File instance function urltoFile(url, filename, mimeType){     mimeType = mimeType || (url.match(/^data:([^;]+);/)||'')[1];     return (fetch(url)         .then(function(res){return res.arrayBuffer();})         .then(function(buf){return new File([buf], filename, {type:mimeType});})     ); }  //Usage example: urltoFile('data:image/png;base64,......', 'a.png') .then(function(file){     console.log(file); }) 

Both works in Chrome and Firefox.

Answer 2

You can create a Blob from your base64 data, and then read it asDataURL:

var img_b64 = canvas.toDataURL('image/png'); var png = img_b64.split(',')[1];  var the_file = new Blob([window.atob(png)],  {type: 'image/png', encoding: 'utf-8'});  var fr = new FileReader(); fr.onload = function ( oFREvent ) {     var v = oFREvent.target.result.split(',')[1]; // encoding is messed up here, so we fix it     v = atob(v);     var good_b64 = btoa(decodeURIComponent(escape(v)));     document.getElementById("uploadPreview").src = "data:image/png;base64," + good_b64; }; fr.readAsDataURL(the_file); 

Full example (includes junk code and console log): http://jsfiddle.net/tTYb8/

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Alternatively, you can use .readAsText, it works fine, and its more elegant.. but for some reason text does not sound right ;)

fr.onload = function ( oFREvent ) {     document.getElementById("uploadPreview").src = "data:image/png;base64,"     + btoa(oFREvent.target.result); }; fr.readAsText(the_file, "utf-8"); // its important to specify encoding here 

Full example: http://jsfiddle.net/tTYb8/3/