生成随机字符串--用于唯一校验

/**
 * 生成随机id
 * @param {*} length
 * @param {*} chars
 */
export function uuid(length, chars) {
    chars =
        chars ||
        '0123456789abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ'
    length = length || 8
    var result = ''
    for (var i = length; i > 0; --i)
        result += chars[Math.floor(Math.random() * chars.length)]
    return result
}