js控制上传文件大小

var isIE = !-[1,];

var target=document.getElementById("fileId");

 if (isIE && !target.files) {

        var filePath = target.value;

        var fileSystem = new ActiveXObject("Scripting.FileSystemObject");

        var file = fileSystem.GetFile (filePath);

        fileSize = file.Size;

    } else {

        fileSize = target.files[0].size;

    }

    var size = fileSize / 1024;

    if(size>4000){

        alert("附件不能大于4M");

        return;

    }