This time I will bring you a preview of HS implementation of txt file upload, what are the precautions for HS to implement txt file upload preview, the following is a practical case, let’s take a look.
I happened to come across this record while working on a project today. Because it is a simple txt file, it only involves text. If you need to preview images, you need to use papaparse and jschardet. There is not much description here.
Form buttonUse js’s onchange="uploadfile()"
Event, the function function code is as follows:
//此处为txt文件上传预览的js代码 function uploadfile(){ var file=$("#txt")[0].files[0]; //判断上传文件是不是txt格式,判断后缀是不是.txt if(file.name.substr(-4).toLocaleLowerCase() != '.txt'){ alert("请上传格式为txt的文件!"); windows.location="test.jsp";//重新定位到上传txt文件页面 } else//如果上传文件是txt文件,则显示文件的预览 { var reader=new FileReader; reader.readAsText(file,'gb2312'); //reader.readAsDataURL(file); reader.onload=function(evt){ var data=evt.target.result; $('#textarea_id').val(data); } } }
The effect is as follows:
Supplement:
js Upload file preview1. FILE API
HTML5 provides two methods, FIle and FileReader, which can read file information and read Get the file.2. example
<p style="border: 1px solid rgb(204, 204, 204); width: 100%; height: 200px; background-size: contain; background-repeat: no-repeat; background-position: center center;"> </p> <br> <p></p> <br> <input> <script> var fileInput = document.getElementById('test-image-file'), info = document.getElementById('test-file-info'), preview = document.getElementById('test-image-preview'); // 监听change事件: fileInput.addEventListener('change', function () { // 清除背景图片: preview.style.backgroundImage = ''; // 检查文件是否选择: if (!fileInput.value) { info.innerHTML = '没有选择文件'; return; } // 获取File引用: var file = fileInput.files[0]; // 获取File信息: info.innerHTML = '文件: ' + file.name + '<br>' + '大小: ' + file.size + '<br>' + '修改: ' + file.lastModifiedDate; if (file.type !== 'image/jpeg' && file.type !== 'image/png' && file.type !== 'image/gif') { alert('不是有效的图片文件!'); return; } // 读取文件: var reader = new FileReader(); reader.onload = function(e) { var data = e.target.result; // 'data:image/jpeg;base64,/9j/4AAQSk...(base64编码)...' preview.style.backgroundImage = 'url(' + data + ')'; }; // 以DataURL的形式读取文件: reader.readAsDataURL(file); }); </script>
3. Explanation
The above code also demonstrates an important feature of JavaScript which is the single-threaded execution mode. In JavaScript, the browser's JavaScript execution engine always executes in single-threaded mode when executing JavaScript code. That is to say, JavaScript code cannot be executed by more than one thread at the same time at any time. You may ask, how does JavaScript executed in single-threaded mode handle multitasking? In JavaScript, multitasking is actually asynchronous call, such as the above code:reader.readAsDataURL(file);
reader.onload = function(e) { // 当文件读取完成后,自动调用此函数: };
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