String builder for JavaScript

StringBuilder.js

function StringBuilder(value) {
    this.strings = new Array();
    this.append(value);
}

StringBuilder.prototype.append = function (value) {
    if (value) {
        this.strings.push(value);
    }
}

StringBuilder.prototype.clear = function () {
    this.strings.length = 0;
}

StringBuilder.prototype.toString = function () {
    return this.strings.join("");
}

StringBuilderUsage.js

var sb = new StringBuilder();

sb.append("This is");
sb.append("much better looking");
sb.append("than using +=");

// joins the string
var myString = sb.toString();

// Cleans out the string buffer in the StringBuilder.
// This effectively makes it empty in case you did not 
// know what cleaning out a buffer in this context
// meant.
sb.clear();

Can you please write more comments for the StringBuilder.js
I am trying to understand how it works.
Thanks