ResizableSlider.js

Slider.implement({

    update: function(step){
        // same as this.set() but doesn't fire any events
        if (!((this.range > 0) ^ (step < this.min))) step = this.min;
        if (!((this.range > 0) ^ (step > this.max))) step = this.max;
        this.step = Math.round(step);
        if (this.previousChange != this.step) this.previousChange = this.step;
        this.knob.setStyle(this.property, this.toPosition(this.step));
        if (this.previousEnd !== this.step) this.previousEnd = this.step;
        return this;
    },
    
    resize: function(){
        // use resize when the slider bar has a new size
        var offset = (this.options.mode == 'vertical') ? 'offsetHeight' : 'offsetWidth';
        this.full = this.element.measure(function(){
            this.half = this.knob[offset] / 2;
            return this.element[offset] - this.knob[offset] + (this.options.offset * 2);
        }.bind(this));
        this.steps = this.options.steps || this.full;
        this.stepSize = Math.abs(this.range) / this.steps;
        this.stepWidth = this.stepSize * this.full / Math.abs(this.range);
        var limit = {};
        this.drag.options.limit[this.axis] = [- this.options.offset, this.full - this.options.offset];
        if (this.options.snap){
            this.drag.options.grid = Math.ceil(this.stepWidth);
            this.drag.options.limit[this.axis][1] = this.full;
        }
        this.update(this.step);
        return this;
    }
    
});

// http://jsfiddle.net/tofu/Dwxht/