详解nodejs实现本地上传图片并预览功能（express4.0+）

<form name='picForm' action = "javascript:;"method="post" encype = "multipart/form-data" >  <input type="file" id="test" id="j_imgfile"></form><div>  <img src="" id="j_imgPic"></div>

$('#j_imgfile').on('change',function(){    // 判断上传文件类型    var objFile = $('#j_imgfile').val();    var objType = objFile.substring(objFile.lastIndexOf(".")).toLowerCase();    var formData = new FormData(document.forms.namedItem("picForm"));    console.log(objType);    if(!(objType == '.jpg'||objType == '.png'))    {      alert("请上传jpg、png类型图片");      return false;    }else{      $.ajax({        type : 'post',        url : '/uploadUserImgPre',        data: formData ,        processData:false,        async:false,        cache: false,          contentType: false,         success:function(re){          re.imgSrc = re.imgSrc.replace('public','');          re.imgSrc = re.imgSrc.replace(////g,'//');          $('#j_imgPic').attr('src',re.imgSrc);        },        error:function(re){          console.log(re);        }      });      }  });

app.post('/uploadUserImgPre',routes.users.uploadUserImgPre);

 exports.uploadUserImgPre = function(req, res, next) { //生成multiparty对象，并配置上传目标路径 var form = new multiparty.Form({uploadDir: './public/files/images'}); form.parse(req, function(err, fields, files) {  var filesTmp = JSON.stringify(files);   if(err){   console.log('parse error: ' + err);  } else {   testJson = eval("(" + filesTmp+ ")");    console.log(testJson.fileField[0].path);   res.json({imgSrc:testJson.fileField[0].path})   console.log('rename ok');  } });}

app.use(express.static(path.join(__dirname, 'public')));