animate.js

// <div id="block"></div>

// #block {
//     position: relative;
//     left: 200px;
//     width: 40px;
//     height: 40px;
//     background-color: #456;
// }

function animate(el, props, duration) {
    var timeDelta = 4;
    var repetitions = Math.floor(duration / timeDelta) || 1;
    var r = 0;
    var computedStyles = getComputedStyle(el);
    var initialStyles = {};
    var deltaStyles = {};
    
    for (var prop in props) {
        initialStyles[prop] = parseFloat(computedStyles[prop]) || 0;
        deltaStyles[prop] = (parseFloat(props[prop]) - initialStyles[prop]) / repetitions;
    }
    
    var move = function () {
        r += 1;
                
        for (var prop in props) {
            el.style[prop] = initialStyles[prop] + deltaStyles[prop] * r + 'px';
        }
        
        if (r >= repetitions) {
            clearInterval(interval);
        }
    };
    
    var interval = setInterval(move, timeDelta);
}

animate(document.getElementById('block'), {
    left: 100,
    top: 20,
    width: 100,
    borderRadius: 5
}, 2000);