js判断上传文件大小

function onUploadImgChange(fileInput) {
	var imgMaxSize = 30 * 1024 * 1024;
	var filePath = fileInput.value;
	if (fileInput.files && fileInput.files[0]) {
		console.log(fileInput.files[0].size);
		if (fileInput.files[0].size > imgMaxSize) {
			alert("图片大于30M，请压缩后上传");
		}
		var xx = fileInput.files[0];
		for (var i in xx) { 
			if(xx[i].size > imgMaxSize) {
				alert("图片大于30M，请压缩后上传");
			}
		}
	} else {
		fileInput.select();
		var url = document.selection.createRange().text;
		try {
			var fso = new ActiveXObject("Scripting.FileSystemObject");
			console.log(fso.GetFile(url).size);
			if (fso.GetFile(url).size) {
				alert("图片大于30M，请压缩后上传");
			}
		} catch (e) {
			alert('如果你用的是ie 请将安全级别调低！');
		}
	}
} 

页面中对应的代码

 <div class="uploader" id="uniform-imageURL">
	                  <input type="file" size="20" value="浏览" class="file" name="upload" id="bannerPic" style="opacity: 0;" οnchange="onUploadImgChange(this);">
	                  <span class="filename" style="-moz-user-select: none;"></span><span class="action" style="-moz-user-select: none;">浏览</span></div>
</div>