用html5编写图片裁切上传，在iphone手机上可能会遇到图片方向错误问题，在此把解决方法和大家分享一下，
用到了html5的 FileReader和Canvas，如果还没有接触的同学，先了解一下其方法。
//此方法为file input元素的change事件 function change(){ var file = this.files[0]; var orientation; //EXIF js 可以读取图片的元信息 https://github.com/exif-js/exif-js EXIF.getData(file,function(){orientation=EXIF.getTag(this,'Orientation'); }); var reader = new FileReader(); reader.onload = function(e) { getImgData(this.result,orientation,function(data){ //这里可以使用校正后的图片data了 }); } reader.readAsDataURL(file);}// @param {string} img 图片的base64// @param {int} dir exif获取的方向信息// @param {function} next 回调方法，返回校正方向后的base64function getImgData(img,dir,next){ var image=new Image(); image.onload=function(){ var degree=0,drawWidth,drawHeight,width,height; drawWidth=this.naturalWidth; drawHeight=this.naturalHeight; //以下改变一下图片大小 var maxSide = Math.max(drawWidth, drawHeight); if (maxSide 1024) {var minSide = Math.min(drawWidth, drawHeight);minSide = minSide / maxSide * 1024;maxSide = 1024;if (drawWidth drawHeight) { drawWidth = maxSide; drawHeight = minSide;} else { drawWidth = minSide; drawHeight = maxSide;} } var canvas=document.createElement('canvas'); canvas.width=width=drawWidth; canvas.height=height=drawHeight; var context=canvas.getContext('2d'); //判断图片方向，重置canvas大小，确定旋转角度，iphone默认的是home键在右方的横屏拍摄方式 switch(dir){//iphone横屏拍摄，此时home键在左侧case 3: degree=180; drawWidth=-width; drawHeight=-height; break;//iphone竖屏拍摄，此时home键在下方(正常拿手机的方向)case 6: canvas.width=height; canvas.height=width; degree=90; drawWidth=width; drawHeight=-height; break;//iphone竖屏拍摄，此时home键在上方case 8: canvas.width=height; canvas.height=width; degree=270; drawWidth=-width; drawHeight=height; break; } //使用canvas旋转校正 context.rotate(degree*Math.PI/180); context.drawImage(this,0,0,drawWidth,drawHeight); //返回校正图片 next(canvas.toDataURL("image/jpeg",.8)); } image.src=img;} 
