生成随机ID且唯一

 var T = [
     {P:11,G:2},
     {P:101,G:7},
     {P:1009,G:26},
     {P:10007,G:59},
     {P:100003,G:242},
     {P:1000003,G:568},
     {P:10000019,G:1792},
     {P:100000007,G:5649},
     {P:2147483647,G:16807},
 ]

 // bits 为位数
 function RandUnique(bits){
     let t = T[bits-1];
     if(!t) {
         throw Error('bits >= 1  and bits <= 9');
     }

     this.p = t.P;
     this.g = t.G;
     this.seed = t.G;
     this.n = 10**bits-1;
 }

 RandUnique.prototype.next = function(){
     let seed = this.seed;
     seed = (this.g * seed) % this.p;
     while( seed > this.n)
         seed = (this.g * seed) % this.p;

     this.seed = seed;
     return seed;
 }

 let ru = new RandUnique(2);
 for(let i=0;i<100;i++){
     console.log(ru.next());
 }

运行结果：