Typewriter effect in plain javascript

typewriter.js

/**
 * content: string to be "typed out"
 * el: parent element to write content in
 * delay: miliseconds between each char
 * 
 * Example usage:
 *      typewriter("Look ma, no hands!", document.getElementById("container"), 100);
 */
var typewriter = function(content, el, delay) {
    var p = document.createElement('p');
    el.appendChild(p);

    var j = 0;
    var interval = window.setInterval(function() {
        p.innerHTML += content.charAt(j);
        j++;
        if (j >= content.length) {
            clearInterval(interval);
        }
    }, delay);
};