js操作一般文件和csv文件

js操作一般文件和csv文件

1. 将文本文件读成字符串

   <input type="file" id="upload">
   
   document.getElementById("upload").addEventListener("change", function() {
       var files = this.files;
       if(files.length == 0) {
           console.log("没有文件");
           return;
       }
   
       var reader = new FileReader();
   
       reader.readAsText(files[0]);
       reader.onload = function(e) {
           console.log("文件内容如下\n"+e.target.result);
       }
   })
   

2. 将读取的图片展示在页面上

   <input type="file" id="upload" accept="image/png">
   
   document.getElementById("upload").addEventListener("change", function() {
       var files = this.files;
       if(files.length == 0) {
           console.log("没有文件");
           return;
       }
   
       var reader = new FileReader();
   
       reader.readAsDataURL(files[0]);
       reader.onload = function(e) {
           var img = new Image();
           img.style.width = "200px";
           img.style.height = "100px"
           img.onload = function() {
               document.body.appendChild(img);
           }
           img.src = e.target.result;
       }
   })
   

3. 处理和下载csv文件

   var blob = new Blob([
       `Year,Make,Model,Description,Price
       1997,Ford,E350,"ac, abs, moon",3000.00
       1999,Chevy,"Venture ""Extended Edition""","",4900.00
       1999,Chevy,"Venture ""Extended Edition, Very Large""",,5000.00
       1996,Jeep,Grand Cherokee,"MUST SELL!
       air, moon roof, loaded",4799.00`
   ])        
   
   if(window.navigator.msSaveOrOpenBlob){
       window.navigator.msSaveBlob(blob, "test.csv");
   }else {
       var a = window.document.createElement("a");
       a.href = window.URL.createObjectURL(blob, {
           type: "text/plain"
       });
       a.download = "test.csv";
       document.body.appendChild(a);
       a.click();
       document.body.removeChild(a);
   }