"+"を使わないプログラミング ref: http://qiita.com/butchi_y/items/3c3e9de3258c6a22ecd0

file0.js

function plus(x, y) {
  return x + y;
}

ans = plus(5, 3);
console.log(ans); // => 8

file1.js

function plus(x, y) {
  return x - -y;
}

file10.txt

function strPlus(str1, str2) {
  return [str1, str2].join('');
}

file11.js

var re = /ab+c/;
console.log(re.test('ac')); // => false
console.log(re.test('abc')); // => true

file12.js

var re = /abb*c/;
console.log(re.test('ac')); // => false
console.log(re.test('abc')); // => true

file13.js

var plusChar = decodeURIComponent('%2B');
var re = new RegExp('ab'.concat(plusChar).concat('c'));
console.log(re.test('ac')); // => false
console.log(re.test('abc')); // => true

file14.js

var plusChar = String.fromCharCode(43);
var re = new RegExp('ab'.concat(plusChar).concat('c'));
console.log(re.test('ac')); // => false
console.log(re.test('abc')); // => true

file2.js

function plus(x, y) {
  return -(-x - y);
}

file3.js

function plus(x, y) {
  for(i=[]; i.length < x; i.push(1)){}
  for(j=[]; j.length < y; j.push(1)){}
  tmp = i.concat(j);
  return tmp.length;
}

file4.js

function plus(x, y) {
  return x-~y-1;
}

file5.js

function incr(x) {
  x++;
  return x;
}

var x, ans;
x = 5;
ans = incr(x);
console.log(ans); // => 6

file6.js

function incr(x) {
  x = -x;
  x--;
  x = -x;
  return x;
}

file7.js

function incr(n) {
  var tmp = [];
  while(tmp.length <= n) {
    tmp.push(1);
  }
  return tmp.length;
}

file8.js

function strPlus() {
  return str1 + str2;
}

var str1, str2, ans;
str1 = 'Thanks, ';
str2 = 'world!';
ans = strPlus(str1, str2);
console.log(ans); // => "Thanks, world!"

file9.js

function strPlus(str1, str2) {
  return str1.concat(str2);
}