随机字符串的生成

function randomString (len = 32){
    const _item = "0123456789abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ";
    let str = "";
    for(let i=0;i<len;i++){
        str += _item.charAt(Math.round(Math.random()*_item.length))
    };
    return str
};