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function map(a, cb) {
    var res = [];

    for (var i = 0, l = a.length; i < l; i++) {
      res.push(cb(a[i], i, a));
    }
    return res;
};

// Example :
let r = map([1,2,3], function (value, index, array) {
  return value*2;
})

console.log(r)
// [ 2, 4, 6 ]