### 算法1 ``` function uuid() {     var s = [];     var hexDigits = "0123456789abcdef";     for (var i = 0; i < 36; i++) {         s[i] = hexDigits.substr(Math.floor(Math.random() * 0x10), 1);     }     s[14] = "4";  // bits 12-15 of the time_hi_and_version field to 0010     s[19] = hexDigits.substr((s[19] & 0x3) | 0x8, 1);  // bits 6-7 of the clock_seq_hi_and_reserved to 01     s[8] = s[13] = s[18] = s[23] = "-";     var uuid = s.join("");     return uuid; } ``` ### 算法2 ``` function guid() {     return 'xxxxxxxx-xxxx-4xxx-yxxx-xxxxxxxxxxxx'.replace(/[xy]/g, function(c) {         var r = Math.random()*16|0, v = c == 'x' ? r : (r&0x3|0x8);         return v.toString(16);     }); } ``` ### 算法3 ``` function guid() {     function S4() {        return (((1+Math.random())*0x10000)|0).toString(16).substring(1);     }     return (S4()+S4()+"-"+S4()+"-"+S4()+"-"+S4()+"-"+S4()+S4()+S4()); } ``` ### 算法4 ``` function uuid(len, radix) {     var chars = '0123456789ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz'.split('');     var uuid = [], i;     radix = radix || chars.length;     if (len) {       // Compact form       for (i = 0; i < len; i++) uuid[i] = chars[0 | Math.random()*radix];     } else {       // rfc4122, version 4 form       var r;       // rfc4122 requires these characters       uuid[8] = uuid[13] = uuid[18] = uuid[23] = '-';       uuid[14] = '4';       // Fill in random data.  At i==19 set the high bits of clock sequence as       // per rfc4122, sec. 4.1.5       for (i = 0; i < 36; i++) {         if (!uuid[i]) {           r = 0 | Math.random()*16;           uuid[i] = chars[(i == 19) ? (r & 0x3) | 0x8 : r];         }       }     }     return uuid.join(''); } ``` ### 第5种 ``` Math.random().toString(36).substring(3, 8) ```