js 生成8位随机数，必须包含大写字母，小写字母和数字。

 1 function generateRandomString() {
 2   var chars = "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789";
 3   var randomString = "";
 4   for (var i = 0; i < 8; i++) {
 5     var randomIndex = Math.floor(Math.random() * chars.length);
 6     randomString += chars.charAt(randomIndex);
 7   }
 8   return randomString;
 9 }
10  var randomString = generateRandomString();
11 console.log(randomString);

 1 function generateRandomString() {
 2   var chars = "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789";
 3   var uppercaseChar = "ABCDEFGHIJKLMNOPQRSTUVWXYZ";
 4   var lowercaseChar = "abcdefghijklmnopqrstuvwxyz";
 5   var numberChar = "0123456789";
 6   var randomString = "";
 7   //首先从每个字符集中选择一个字符
 8   randomString += uppercaseChar.charAt(Math.floor(Math.random() * uppercaseChar.length));
 9   randomString += lowercaseChar.charAt(Math.floor(Math.random() * lowercaseChar.length));
10   randomString += numberChar.charAt(Math.floor(Math.random() * numberChar.length));
11   //随机选择其他字符
12   for (var i = 3; i < 8; i++) {
13     var randomIndex = Math.floor(Math.random() * chars.length);
14     randomString += chars.charAt(randomIndex);
15   }
16   //对字符串进行随机排序
17   randomString = randomString.split('').sort(function(){
18       return 0.5-Math.random();
19   }).join('');
20   return randomString;
21 }
22 //测试代码
23 console.log(generateRandomString()); 

// 最后，为确保生成的字符串具有随机性，使用 split() 方法将字符串转换为字符数组，再将此数组随机排序，并使用 join() 方法将排序后的字符重新组成一个字符串。这种方法可以防止字符选择过于一致，从而增强随机性。

 1 function generateRandomString() {
 2   var chars = "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789";
 3   var length = 8;
 4   var result = "";
 5   var hasUpperCase = false;
 6   var hasLowerCase = false;
 7   var hasNumber = false;
 8    for (var i = 0; i < length; i++) {
 9     var randomChar = chars.charAt(Math.floor(Math.random() * chars.length));
10     result += randomChar;
11     if ("ABCDEFGHIJKLMNOPQRSTUVWXYZ".indexOf(randomChar) != -1) {
12       hasUpperCase = true;
13     } else if ("abcdefghijklmnopqrstuvwxyz".indexOf(randomChar) != -1) {
14       hasLowerCase = true;
15     } else if ("0123456789".indexOf(randomChar) != -1) {
16       hasNumber = true;
17     }
18   }
19    if (hasUpperCase && hasLowerCase && hasNumber) {
20     return result;
21   } else {
22     return generateRandomString();
23   }
24 }

 1 function generateRandomString() {
 2     var chars = "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789";
 3     var uppercase = false, lowercase = false, digit = false;
 4     var randomStr = '';
 5     while (!(uppercase && lowercase && digit) || randomStr.length < 8) {
 6         var randomNum = Math.floor(Math.random() * chars.length);
 7         randomStr += chars.substring(randomNum, randomNum + 1);
 8         uppercase = /[A-Z]/.test(randomStr);
 9         lowercase = /[a-z]/.test(randomStr);
10         digit = /\d/.test(randomStr);
11     }
12     return randomStr;
13 }