1、JS图片转base64编码实现
function convertImgToBase64(url, callback, outputFormat){ var canvas = document.createElement('CANVAS'), ctx = canvas.getContext('2d'), img = new Image; img.crossOrigin = 'Anonymous'; img.onload = function(){ canvas.height = img.height; canvas.width = img.width; ctx.drawImage(img,0,0); var dataURL = canvas.toDataURL(outputFormat || 'image/png'); callback.call(this, dataURL); canvas = null; }; img.onerror = function(){ canvas.height = img.height; canvas.width = img.width; ctx.drawImage(img,0,0); var dataURL = canvas.toDataURL(outputFormat || 'image/png'); callback.call(this, dataURL); canvas = null; }; img.src = url; if (img.complete) { // 如果图片已经存在于浏览器缓存，直接调用回调函数 canvas.height = img.height; canvas.width = img.width; ctx.drawImage(img,0,0); var dataURL = canvas.toDataURL(outputFormat || 'image/png'); callback.call(this, dataURL); canvas = null; return; // 直接返回，不用再处理onload事件 } }2、代码分析1）上述中的onload会在图片加载成功后调用
2）上述的onerror会在图片地址为无效地址的时候，即图片加载失败后调用
3）img.complete用于如果浏览器缓存了图片，则这个值true，onload、onerror都不会被调用了，此时直接进行处理即可
