Other Polyfills to Practice for Interviews

Other Polyfills to Practice for Interviews

map Polyfill

Array.prototype.myMap = function (callback, thisArg) {
  const result = [];
  for (let i = 0; i < this.length; i++) {
    result.push(callback.call(thisArg, this[i], i, this));
  }
  return result;
};

filter Polyfill

Array.prototype.myFilter = function (callback, thisArg) {
  const result = [];
  for (let i = 0; i < this.length; i++) {
    if (callback.call(thisArg, this[i], i, this)) result.push(this[i]);
  }
  return result;
};

reduce Polyfill

Array.prototype.myReduce = function (callback, initialValue) {
  let acc = initialValue;
  let start = 0;
  if (initialValue === undefined) {
    if (this.length === 0) throw new TypeError("Reduce of empty array with no initial value");
    acc = this[0];
    start = 1;
  }
  for (let i = start; i < this.length; i++) {
    acc = callback(acc, this[i], i, this);
  }
  return acc;
};

Promise.all Polyfill

function myPromiseAll(promises) {
  return new Promise((resolve, reject) => {
    const results = [];
    let completed = 0;
    promises.forEach((promise, index) => {
      Promise.resolve(promise).then((value) => {
        results[index] = value;
        if (++completed === promises.length) resolve(results);
      }).catch(reject);
    });
  });
}

The Takeaway

Practice these polyfills: map (loop, call callback, push result), filter (loop, call callback, push if truthy), reduce (handle initial value, loop, update accumulator), and Promise.all (resolve all, count completed, reject on any failure). These are common interview questions.