lz77 decompression

function lz77_decompress(input, dictlen){
    let output="", drl=0, dl=dictlen;
    for(let i=0; i<input.length; i++){
        if( input[i].length==0 ){
            output+=input[i].char;
        }else{
            let j=drl-dl+input[i].index, k=j;
            let l2=input[i].length+input[i].index-Math.max(0, dl-drl),
                len=drl-dl+Math.min(dl, l2);
            while( j<len ){
                output+=output[j];
                j++;
            }
            while( j<l2 ){
                output+=output[k];
                k++;
                j++;
            }
            output+=input[i].char;
        }
        drl+=input[i].length+1;
    }
    return output;
}