js缓动函数

tween: {
            easeInQuad: function(pos){
                return Math.pow(pos, 2);
            },

            easeOutQuad: function(pos){
                return -(Math.pow((pos-1), 2) -1);
            },

            easeInOutQuad: function(pos){
                if ((pos/=0.5) < 1) return 0.5*Math.pow(pos,2);
                return -0.5 * ((pos-=2)*pos - 2);
            },

            easeInCubic: function(pos){
                return Math.pow(pos, 3);
            },

            easeOutCubic: function(pos){
                return (Math.pow((pos-1), 3) +1);
            },

            easeInOutCubic: function(pos){
                if ((pos/=0.5) < 1) return 0.5*Math.pow(pos,3);
                return 0.5 * (Math.pow((pos-2),3) + 2);
            },

            easeInQuart: function(pos){
                return Math.pow(pos, 4);
            },

            easeOutQuart: function(pos){
                return -(Math.pow((pos-1), 4) -1)
            },

            easeInOutQuart: function(pos){
                if ((pos/=0.5) < 1) return 0.5*Math.pow(pos,4);
                return -0.5 * ((pos-=2)*Math.pow(pos,3) - 2);
            },

            easeInQuint: function(pos){
                return Math.pow(pos, 5);
            },

            easeOutQuint: function(pos){
                return (Math.pow((pos-1), 5) +1);
            },

            easeInOutQuint: function(pos){
                if ((pos/=0.5) < 1) return 0.5*Math.pow(pos,5);
                return 0.5 * (Math.pow((pos-2),5) + 2);
            },

            easeInSine: function(pos){
                return -Math.cos(pos * (Math.PI/2)) + 1;
            },

            easeOutSine: function(pos){
                return Math.sin(pos * (Math.PI/2));
            },

            easeInOutSine: function(pos){
                return (-.5 * (Math.cos(Math.PI*pos) -1));
            },

            easeInExpo: function(pos){
                return (pos==0) ? 0 : Math.pow(2, 10 * (pos - 1));
            },

            easeOutExpo: function(pos){
                return (pos==1) ? 1 : -Math.pow(2, -10 * pos) + 1;
            },

            easeInOutExpo: function(pos){
                if(pos==0) return 0;
                if(pos==1) return 1;
                if((pos/=0.5) < 1) return 0.5 * Math.pow(2,10 * (pos-1));
                return 0.5 * (-Math.pow(2, -10 * --pos) + 2);
            },

            easeInCirc: function(pos){
                return -(Math.sqrt(1 - (pos*pos)) - 1);
            },

            easeOutCirc: function(pos){
                return Math.sqrt(1 - Math.pow((pos-1), 2))
            },

            easeInOutCirc: function(pos){
                if((pos/=0.5) < 1) return -0.5 * (Math.sqrt(1 - pos*pos) - 1);
                return 0.5 * (Math.sqrt(1 - (pos-=2)*pos) + 1);
            },

            easeOutBounce: function(pos){
                if ((pos) < (1/2.75)) {
                    return (7.5625*pos*pos);
                } else if (pos < (2/2.75)) {
                    return (7.5625*(pos-=(1.5/2.75))*pos + .75);
                } else if (pos < (2.5/2.75)) {
                    return (7.5625*(pos-=(2.25/2.75))*pos + .9375);
                } else {
                    return (7.5625*(pos-=(2.625/2.75))*pos + .984375);
                }
            },

            easeInBack: function(pos){
                var s = 1.70158;
                return (pos)*pos*((s+1)*pos - s);
            },

            easeOutBack: function(pos){
                var s = 1.70158;
                return (pos=pos-1)*pos*((s+1)*pos + s) + 1;
            },

            easeInOutBack: function(pos){
                var s = 1.70158;
                if((pos/=0.5) < 1) return 0.5*(pos*pos*(((s*=(1.525))+1)*pos -s));
                return 0.5*((pos-=2)*pos*(((s*=(1.525))+1)*pos +s) +2);
            },

            elastic: function(pos) {
                return -1 * Math.pow(4,-8*pos) * Math.sin((pos*6-1)*(2*Math.PI)/2) + 1;
            },

            swingFromTo: function(pos) {
                var s = 1.70158;
                return ((pos/=0.5) < 1) ? 0.5*(pos*pos*(((s*=(1.525))+1)*pos - s)) :
                0.5*((pos-=2)*pos*(((s*=(1.525))+1)*pos + s) + 2);
            },

            swingFrom: function(pos) {
                var s = 1.70158;
                return pos*pos*((s+1)*pos - s);
            },

            swingTo: function(pos) {
                var s = 1.70158;
                return (pos-=1)*pos*((s+1)*pos + s) + 1;
            },

            bounce: function(pos) {
                if (pos < (1/2.75)) {
                    return (7.5625*pos*pos);
                } else if (pos < (2/2.75)) {
                    return (7.5625*(pos-=(1.5/2.75))*pos + .75);
                } else if (pos < (2.5/2.75)) {
                    return (7.5625*(pos-=(2.25/2.75))*pos + .9375);
                } else {
                    return (7.5625*(pos-=(2.625/2.75))*pos + .984375);
                }
            },

            bouncePast: function(pos) {
                if (pos < (1/2.75)) {
                    return (7.5625*pos*pos);
                } else if (pos < (2/2.75)) {
                    return 2 - (7.5625*(pos-=(1.5/2.75))*pos + .75);
                } else if (pos < (2.5/2.75)) {
                    return 2 - (7.5625*(pos-=(2.25/2.75))*pos + .9375);
                } else {
                    return 2 - (7.5625*(pos-=(2.625/2.75))*pos + .984375);
                }
            },

            easeFromTo: function(pos) {
                if ((pos/=0.5) < 1) return 0.5*Math.pow(pos,4);
                return -0.5 * ((pos-=2)*Math.pow(pos,3) - 2);
            },

            easeFrom: function(pos) {
                return Math.pow(pos,4);
            },

            easeTo: function(pos) {
                return Math.pow(pos,0.25);
            },

            linear:  function(pos) {
                return pos
            },

            sinusoidal: function(pos) {
                return (-Math.cos(pos*Math.PI)/2) + 0.5;
            },

            reverse: function(pos) {
                return 1 - pos;
            },

            mirror: function(pos, transition) {
                transition = transition || tween.sinusoidal;
                if(pos<0.5)
                    return transition(pos*2);
                else
                    return transition(1-(pos-0.5)*2);
            },

            flicker: function(pos) {
                var pos = pos + (Math.random()-0.5)/5;
                return tween.sinusoidal(pos < 0 ? 0 : pos > 1 ? 1 : pos);
            },

            wobble: function(pos) {
                return (-Math.cos(pos*Math.PI*(9*pos))/2) + 0.5;
            },

            pulse: function(pos, pulses) {
                return (-Math.cos((pos*((pulses||5)-.5)*2)*Math.PI)/2) + .5;
            },

            blink: function(pos, blinks) {
                return Math.round(pos*(blinks||5)) % 2;
            },

            spring: function(pos) {
                return 1 - (Math.cos(pos * 4.5 * Math.PI) * Math.exp(-pos * 6));
            },

            none: function(pos){
                return 0
            },

            full: function(pos){
                return 1
            }
        }