smooth scroll

app.js

// for jquery

$( document ).ready(function() {
    $(".smoothScroll").on('click', function(e){
        smoothScroll(e);
	})	
});

smoothScroll.js

window.jump = function(target, options) {
    options = options || {};
    var t = document.querySelector(target);
    if (t == null) return;
    var start = window.pageYOffset,
        opt = {
            duration: options.duration || 100,
            offset: options.offset || 0,
            callback: options.callback,
            easing: options.easing || easeInOutQuad
        },
        distance = typeof target === 'string'
            ? opt.offset + t.getBoundingClientRect().top
            : target,
        duration = typeof opt.duration === 'function'
            ? opt.duration(distance)
            : opt.duration,
        timeStart, timeElapsed
    ;
    
    requestAnimationFrame(function(time) { timeStart = time; loop(time); });
    
    function loop(time) {
        timeElapsed = time - timeStart;

        window.scrollTo(0, opt.easing(timeElapsed, start, distance, duration));

        if (timeElapsed < duration)
            requestAnimationFrame(loop)
        else
            end();
    }

    function end() {
        window.scrollTo(0, start + distance);
        if (typeof opt.callback === 'function')
            opt.callback();
    }
    
    // Robert Penner's easeInOutQuad - http://robertpenner.com/easing/
    function easeInOutQuad(t, b, c, d)  {
        t /= d / 2
        if(t < 1) return c / 2 * t * t + b
        t--
        return -c / 2 * (t * (t - 2) - 1) + b
    } 
}

window.smoothScroll = function (e, offset) {        
        e.stopPropagation();
        e.preventDefault();
        offset = offset || -50;
        var vm = this;
        var hash = e.target.hash || e.currentTarget.hash

        jump(hash, {
            duration: 400,
            offset: offset,            
            callback: function() {}
        });
    }