<div class="pass-box">
<input type="password" name="pass" />
<i state="off"></i>
</div>

.pass-box {
width: 300px;
margin: 30px auto;
position: relative;
}
.pass-box input {
border: #cccccc 1px solid;
background-color: #fff;
color: #666;
padding: 10px;
width: 100%;
box-sizing: border-box;
}
.pass-box i{
display: inline-block;
width: 30px;
height: 30px;
position: absolute;
right: 5px;
top:5px;
background-image: none;
background-size: 200% 200%;
background-position: center;
}

var ele_pass_box = document.getElementsByTagName("div")[0];
var ele_pass = ele_pass_box.getElementsByTagName("input")[0];
var ele_eye = ele_pass_box.getElementsByTagName("i")[0];
ele_eye.onclick = function () {
var state = this.getAttribute("state");
if(state === "off") {
ele_pass.setAttribute("type", "text");
ele_eye.setAttribute("state", "on");
ele_eye.style.opacity = 0.2;
} else {
ele_pass.setAttribute("type", "password");
ele_eye.setAttribute("state", "off");
ele_eye.style.opacity = 1;
}
}