<input type="file" id="picFile" /> 

 function readFile() {
     var obj = document.getElementById("picFile");
     if (obj.files.length < 1) {
         console.log("请选择文件");
         return;
     }
     var file = obj.files[0];
     if (!/image\/\w+/.test(file.type)) {
         console.log("请确保文件为图像类型");
         return;
     }
     var reader = new FileReader();
     reader.readAsDataURL(file);
     reader.onload = function (e) {
         //console.log(e.target.result);
         console.log(this.result);
     }
 }