프로그래머스| 신규 아이디 추천

function solution(new_id) {
    let arr=new_id.toLowerCase().split('')
    .filter(e=>e==='-'||e==='_'||e==='.'||(e.charCodeAt(0)>=97&&e.charCodeAt(0)<=122)||isNaN(Number(e))===false);
    
    let arr2=[];
    for(let i=0;i<arr.length;i++){
        if(arr[i]==='.'&&arr[i+1]==='.'){
            continue;
        }else{
            arr2.push(arr[i])
        }
            
    }
    if(arr2[0]==='.'){
        arr2.shift();
    }  
    if(arr2[arr2.length-1]==='.'){
        arr2.pop();
    }
    if(arr2.length===0){
        arr2.push('a')
    }
    if(arr2.length>15){
       arr2=arr2.slice(0,15);
    }
    if(arr2[arr2.length-1]==='.'){//자르고 나서 마지막에 '.'일 경우
        arr2.pop();
    }
    if(arr2.length<=2){
        while(arr2.length!==3){
            arr2.push(arr2[arr2.length-1])
        }
    }
    return arr2.join('');
}