效果：
代码：
<style>
.inputBox {
width: 100px;
height: 50px;
background: green;
color: white;
font-size: 16px;
text-align: center;
line-height: 50px;
border-radius: 4px;
cursor: pointer;
}
</style>
<body>
<form action="" method="" enctype='multipart/form-data'>
<label for='file' class='inputlabelBox'>
<div class="inputBox">上传文件</div>
</label>
<input type="file" name="myfile" id='file' style="display:none;" />
</form>
<img src="" id="img" width="300" />
<script>
var inputlabelBox = document.querySelector('.inputlabelBox');
var myfile = document.querySelector('#file');
var img = document.querySelector('#img');
myfile.onchange = function () {
var my_file = this.files[0];
console.log(file.files[0]);
console.log(file.files[0].name);
var reader = new FileReader();
reader.readAsDataURL(my_file);
reader.onload = function () {
console.log(this.result);
img.src = this.result;
}
}
</script>
</body>