github.com.js

function clone(o) {
    return JSON.parse(JSON.stringify(o));
}

function insert_fds_button(imageAttributes, params){
    // check for the correct page
    if (! (!!document.querySelector(params.existsInPage))) {
        return;
    }
    var img         = document.createElement('img'),
    button          = document.createElement('button'),
    wrapperDiv      = document.querySelector(params.wrapper),
    handleClick     = function(e){
        var textarea = document.querySelector(params.form + ' ' + params.textarea),
        form     = document.querySelector(params.form);
        e.preventDefault();
        if (-1 == textarea.value.indexOf(params.text)) {
            textarea.value = textarea.value + "\n" + params.text + "\n";
	}

        if (params.submit) {
            //console.log('form will submit');
            //console.log(form);
            form.submit();
            textarea.value = '';
	}
    },
    key;

    for(key in imageAttributes){
        img.setAttribute(key, imageAttributes[key]);
    }
    button.setAttribute('class', 'btn ' + params.buttonclass );
    button.appendChild(img);
    button.addEventListener('click', handleClick, false);
    wrapperDiv.appendChild(button);
}

var imageAttributes = {
    width: "20",
    height: "20",
    align: "absmiddle",
    src: "https://assets-cdn.github.com/images/icons/emoji/thumbsup.png",
    alt: "Alrite ! Ship It!",
    title: "Alrite ! Ship It!",
    class: "emoji"
};

var params = {
    wrapper: '.js-new-comment-form .form-actions div',
    existsInPage: 'div.view-pull-request',
    submit: true,
    form: '.js-new-comment-form',
    textarea: '.js-comment-field',
    text: ':thumbsup:',
    buttonclass: 'btn-info'
};


imageAttributes.src = "https://assets-cdn.github.com/images/icons/emoji/thumbsup.png";
imageAttributes.title= "Alrite ! Ship It!";
imageAttributes.alt= "Alrite ! Ship It!";

insert_fds_button(clone(imageAttributes), clone(params));

params.text = '[Radioactive reviewers: @umesh-fds, @nbayyana, @sanjay-fds, @davec-fds, @premkumr]';
imageAttributes.src = "http://www.ipharmd.net/images/medium/tn_round_radioactive_symbol_clipart.png";
imageAttributes.title= "Radioactive Review";
imageAttributes.alt= "Radioactive Review";
insert_fds_button(clone(imageAttributes), clone(params));

params.text = 'Retest this please';
params.buttonclass = 'btn-danger';
imageAttributes.src = "https://assets-cdn.github.com/images/icons/emoji/repeat.png"
imageAttributes.title= "Retest this";
imageAttributes.alt= "Retest";
insert_fds_button(clone(imageAttributes), clone(params));