https://none-none1.github.io/Interpret-Esolangs-Online/plusintoutput.js

1function plusintoutput(program,input){
2    var x=0,output='';
3    while(program.length){
4        if(program[0]=='+'){
5            var a=0;
6            program=program.slice(1);
7            if(!'0123456789'.includes(program[0])){
8                x=(x+1)%256;
9            }else{
10                while('0123456789'.includes(program[0])){
11                    a=a*10+program.charCodeAt(0)-48;
12                    program=program.slice(1);
13                }
14                x=(x+a)%256;
15            }
16        }else if(program[0]=='.'){
17            output+=String.fromCharCode(x);
18            program=program.slice(1);
19        }else{
20            program=program.slice(1);
21        }
22    }
23    return output;
24}