markdown_keyboard_shortcuts.user.js

// ==UserScript==
// @name        SO_like_keyboards_shortcuts
// @namespace   sputnick
// @include     https://github.com/*
// @include     https://gist.github.com/*
// @include     https://*.slack.com/*
// @include     https://stackoverflow.com/*
// @include     hhttps://serverfault.com/*
// @include     https://*stackexchange.com/*
// @include     https://askubuntu.com/*
// @include     https://superuser.com/*

// @version     1
// @grant       none
// ==/UserScript==

// http://meta.stackexchange.com/a/272565/203970
// TODO need to work with gist

var id, name;
if (document.location.href.search(/gist\.github\.com/) > 0 ) { //TODO to be fixed
    id = '#blob_contents';
    name = 'gist';
}
else if (document.location.href.search(/github\.com.*new$/) > 0 ) {
    id = '#issue_body';
    name = 'github';
}
else if (document.location.href.search(/github\.com\/.*\/issues\/[0-9]+/) > 0 ) {
    id = '#new_comment_field';
    name = 'github';
}
else if (document.location.href.search(/slack\.com/) > 0 ) {
    id = '#message-input';
    name = 'slack';
}
else if (document.location.href.search(/(stackoverflow|stackexchange|superuser|askubuntu|serverfault)/) > 0 ) {
    id = '[id^=wmd-input]';
    name = 'stack';
}

(function() {
    document.addEventListener('keydown', function(e){
        //window.alert(e.which);

        if (document.activeElement.tagName == "TEXTAREA") {
            // ctrl+0 [tag:]
            if (e.ctrlKey && e.which == 96) {
                override(e);
                wrapText(id, '[tag:', ']');
            }
            // ctrl+b: bold
            if (e.ctrlKey && e.which == 66) {
                override(e);
                if (name == 'slack') { wrapText(id, '*', '*'); }
                if (name == 'github' || name == 'gist') { wrapText(id, '**', '**'); }
            }
            // ctrl+i: emphasis
            if (e.ctrlKey && e.which == 73) {
                override(e);
                wrapText(id, '_', '_');
            }
            // ctrl+k: code
            if (e.ctrlKey && e.which == 75) {
                override(e);
                wrapText(id, '`', '`');
            }
            // ctrl+l: link
            if (name !== 'stack' && e.ctrlKey && e.which == 76) {
                override(e);
                var p = window.prompt("Link paste bellow");
                wrapText(id, '[', ']('+p+')');
            }
        }
    }, true);
})();

function wrapText(elementID, openTag, closeTag) {
    var textArea = document.querySelector(elementID);
    var len = textArea.value.length;
    var start = textArea.selectionStart;
    var end = textArea.selectionEnd;
    var selectedText = textArea.value.substring(start, end);
    if (openTag == '`' && selectedText.search(/\n/) > 0 ) {
        openTag = '```\n';
        closeTag = '\n```';
    }
    var replacement = openTag + selectedText + closeTag;
    textArea.value = textArea.value.substring(0, start) + replacement + textArea.value.substring(end, len);
}

function override(e) {
    e.stopImmediatePropagation();
    e.cancelBubble = true;
    e.preventDefault();
}