util.js
function rand16Num(len) {
    let result = [];
    for (let i = 0; i < len; i++) {
        result.push('0123456789abcdef'.charAt(
            Math.floor(Math.random() * 16))
        );
    }
    return result.join('');
}
function rand16Num(len) {
    let result = [];
    for (let i = 0; i < len; i++) {
        result.push('0123456789abcdef'.charAt(
            Math.floor(Math.random() * 16))
        );
    }
    return result.join('');
}
function rand16Num ( len ) { let result = [ ] ; for ( let i = 0 ; i < len ; i ++ ) { result . push ( '0123456789abcdef' . charAt ( Math . floor ( Math . random ( ) * 16 ) ) ) ; } return result . join ( '' ) ; }
Generates a random GUID legal string of the given length.

@param {number} len 要生成串的长度

@return {string} 指定长度的16进制数随机串
Generates a random GUID legal string of the given length .