SOURCE

var obj = new Fun();
// obj.run = 3;
function Fun(){
    this.run = 1;
}
Fun.prototype.run = 2;

obj.__proto__.run = 4;

Object.prototype.run = 5;


console.log(obj.run);

<ul class="clear-fix">
    <li></li>
    <li></li>
    <li></li>
</ul>

* {
    margin: 0;
    padding: 0;
    box-sizing: border-box;
}

.clear-fix {
    border: 15px solid red;
    overflow: hidden;
}
/*
.clear-fix::after{
    content: "";
    clear: both;
    display: block;
} */

li{
    width: 50px;
    height: 50px;
    background-color: gray;
    float: left;
    list-style: none;
}