Find the difference in two array.

array_diff.js

var array1 = [1, 3, 4];
var array2 = [5, 4, 2];

var existing = [];

for (var i = 0; i < array1.length; i++) {
    var key = array1[i];
    existing[key] = true;
}

for (var i = 0; i < array2.length; i++) {
    var key = array2[i];
    if (existing[key]) {
        delete existing[key];
    } else {
        existing[key] = true;
    }
}

var differences = [];
for (var k in existing) {
    differences.push(k);
}

console.log(differences);