JS檢測上傳圖片大小

<input type="text" size="4" value="100" name="fileSizeLimit" id="fileSizeLimit"/> K <input type="file" name="file1" id="file1" size="40" onchange="changeSrc(this)"/> <img src="about:blank" id="fileChecker" style="display:none;">     <script type="text/javascript" defer> var oFileChecker = document.getElementById("fileChecker");     function changeSrc(filePicker) {     oFileChecker.src = filePicker.value; }     oFileChecker.onreadystatechange = function () {     if (oFileChecker.readyState == "complete")     {         checkSize();     } }     function checkSize() {     var limit  = document.getElementById("fileSizeLimit").value * 1024;     alert((Number(oFileChecker.fileSize)/1024).toFixed(2)+"k")     if (oFileChecker.fileSize > limit)     {           alert("too large");     }     else     {         alert("ok");     } } </script>