huffman coding

function huffman_codes(str){
    let occ = [];
    for(let i=0; i<str.length; i++){
        let j=0;
        for(; j<occ.length; j++){
            if( occ[j].letter==str[i] ){
                break;
            }
        }
        if( j==occ.length ){
            occ.push( {
                right_child: null, left_child: null,
                letter: str[i], duplication: 1
            } );
        }else{
            occ[j].duplication++;
        }
    }
    while( occ.length!=1 ){
        occ.sort( function(a, b){
            return a.duplication-b.duplication;
        } );
        let node=occ[0], node2=occ[1], parent;
        if( node.duplication<node2.duplication ){
            parent={
                right_child: node,
                left_child: node2,
                letter: null,
                duplication: node.duplication+node2.duplication
            };
        }else{
            parent={
                right_child: node2,
                left_child: node,
                letter: null,
                duplication: node.duplication+node2.duplication
            };
        }
        occ.splice(0,2);
        occ.unshift(parent);
    }
    let codes=[];
    _huffman_encode(occ[0], "", codes);
    return codes;
}

function _huffman_encode(par, str, t) {
    if( par.letter==null ){
        _huffman_encode(par.left_child, str+0, t);
        _huffman_encode(par.right_child, str+1, t);
    }
    else
        t.push({ letter: par.letter, code: str});
}

function huffman_encode(str, codes){
    let encode="";
    for(let i=0; i<str.length; i++){
        for(let j=0; j<codes.length; j++){
            if( codes[j].letter==str[i] ){
                encode+=codes[j].code;
                break;
            }
        }
    }
    return encode;
}

function huffman_decode(encode, codes) {
    let str="", decode="";
    for(let i=0; i<encode.length; i++){
        str+=encode[i];
        for(let j=0; j<codes.length; j++){
            if( codes[j].code==str ){
                decode+=codes[j].letter;
                str="";
                break;
            }
        }
    }
    return decode;
}