一部分が重複している２つの配列の、差分を取得する（JavaScript) - Qiita

function arr_diff (a1, a2) { var a = [], diff = []; for (var i = 0; i < a1.length; i++) { a[a1[i]] = true; } for (var i = 0; i < a2.length; i++) { if (a[a2[i]]) { delete a[a2[i]]; } else { a[a2[i]] = true; } } for (var k in a) { diff.push(k); } return diff; } console.log(arr_diff(['a', 'b'], ['a', 'b', 'c', 'd'])); console.log(arr_diff("abcd", "abcde")); console.log(arr_diff("zxc", "zxc"));