A simple javascript function to toggle a class on/off. No need for jquery to build a simple responsive menu or somewhat.

toggle.js

toggleClass = function( el, className ) {
 
    if ( el.classList ) {

        el.classList.toggle( className );
 
    } else {

        var classes = el.className.split( ' ' );
        var existingIndex = classes.indexOf( className );
 
        if (existingIndex >= 0) {
            classes.splice( existingIndex, 1 );
        } else {
            classes.push( className );
        }
 
        el.className = classes.join( ' ' );
        
    }

};


/*

EXAMPLE USAGE:

var btn = document.getElementById('menu').getElementsByClassName('toggle')[0];
var tgt = document.getElementById('menu').getElementsByClassName('target')[0];

*/

var btn = document.getElementById( 'menu' );

btn.onclick = function () {
    toggleClass( this, 'active' );
}