上传图片的本地预览

上传图片的本地预览

<input type="file" id='uploadImg'>
<img src="" alt="" class="imgShow">

//上传图片本地预览
        $('#uploadImg').on('change',function(){
            var file = $(this)
            var fileObj = file[0];  //获取当前元素
            var dataURL;
            var windowURL = window.URL;
            if(fileObj.files[0]){
                dataURL = windowURL.createObjectURL(fileObj.files[0])   //创建一个新的对象URL,该对象URL可以代表某一个指定的File对象或Blob对象.
                $('.imgShow').attr('src',dataURL);
            }
            else{
                dataURL = file.val();
                console.log(dataURL)
                $('.imgShow').style.filter = 'progid:DXImageTransform.Micsoft.AlphaImageLoader(sizingMethod = scale)'
                $('.imgShow').filters.item('DXImageTransform.Microsoft.AlphaImageLoader').src = dataURL;
            }
            $.ajaxFileUpload({
             url:"",
             fileElementId: "uploadImg",
             dataType: "string",
             success: function(data) {
                 //图片路径
                 $('.imgShow').attr("src",data);
             }
         });

        })

上传图片本地预览 + 压缩上传

<input type="file" accept="image/*"  class='file' id='uploadImg' value=''>      
<img src="" class='imgShow' />

 $('#uploadImg').on('change',function(event){
        if(!isCanvasSupported){  
                return;
         }else{  
            compress(event, function(base64Img){  
                $(".imgShow").attr("src",base64Img);  
                console.log(base64Img);  //压缩的base64的图片格式，通过ajax上传
                //点击图片放大
                    $('.imgShow').click(function(){
                        var width = $('.imgShow').width();    //通过判断元素的宽度
                        console.log(width)          
                        if(width == '200'){
                            $('.mengban').show();
                            $('.imgShow').addClass('changeImg')
                        }
                        $('.mengban').click(function(){
                            $('.imgShow').removeClass('changeImg')
                            $('.mengban').hide();
                        })
                    })
                     ajax('qnl_app/tes_ac_img',{'base64Img':base64Img},function(date){  
                        console.log(JSON.stringify(date)); 
                        $('.imgShow').attr("src",data); 
                     });  
                });  
             }  
      })

压缩图片用的js方法如下：

//判断是否存在画布  
function isCanvasSupported() {  
    var elem = document.createElement('canvas');  
    return !!(elem.getContext && elem.getContext('2d'));  
}  

//压缩方法  
function compress(event, callback) {  
    if ( typeof (FileReader) === 'undefined') {  
        console.log("当前浏览器内核不支持base64图标压缩");  
        //调用上传方式  不压缩  
    } else {  
        try {  
            var file = event.currentTarget.files[0];  
             if(!/image\/\w+/.test(file.type)){     
                    alert("请确保文件为图像类型");    
                    return false;    
             }   
            var reader = new FileReader();  
            reader.onload = function (e) {  
            var image = $('<img/>');  
            image.load(function () {  
            console.log("开始压缩");  
            var square = 700;  
            var canvas = document.createElement('canvas');  
            canvas.width = square;  
            canvas.height = square;  
            var context = canvas.getContext('2d');  
            context.clearRect(0, 0, square, square);  
            var imageWidth;  
            var imageHeight;  
            var offsetX = 0;  
            var offsetY = 0;  
            if (this.width > this.height) {  
              imageWidth = Math.round(square * this.width / this.height);  
              imageHeight = square;  
              offsetX = - Math.round((imageWidth - square) / 2);  
            } else {  
              imageHeight = Math.round(square * this.height / this.width);  
              imageWidth = square;  
              offsetY = - Math.round((imageHeight - square) / 2);  
            }  
            context.drawImage(this, offsetX, offsetY, imageWidth, imageHeight);  
            var data = canvas.toDataURL('image/jpeg');  
                //压缩完成执行回调  
               callback(data);  
            });  
            image.attr('src', e.target.result);  
            };  
            reader.readAsDataURL(file);  
        } catch(e) {  
            console.log("压缩失败!");  
            //调用上传方式  不压缩  
        }  
    }  
}