api : rate
var RateRandom = require('rate-random');
RateRandom.rate({a:1,b:2,c:3});//a,b,c按概率1/6,2/6,3/6抽取
RateRandom.rate({a:'20%',b:'20%',c:'30%'});//a,b,c按概率2/7,2/7,3/7抽取
api : randomArr
var RateRandom = require('rate-random');
var a = [1,2,3];
// return Array
RateRandom.randomArr(a);//从1，2，3中随机抽取一个
RateRandom.randomArr(a,2);////从1，2，3中随机抽取两个
RateRandom.randomArr([{a:'a',weight:10},{b:'b',weight:20},{c:'c',weight:1}],'weight');随机抽取一个，以weight为权重
RateRandom.randomArr([{a:'a',weight:10},{b:'b',weight:20},{c:'c',weight:1}],2,'weight');随机抽取两个，以weight为权重
RateRandom.randomArr([{a:'a',weight:10},{b:'b',weight:20},{c:'c',weight:1}],2);随机抽取两个
RateRandom.randomArr([{a:'a',weight:'10%'},{b:'b',weight:'20%'},{c:'c',weight:'1%'}],2);随机抽取两个