The answer
No. map returns a new array with the results. The original array is unchanged. A polyfill should also not mutate the original array.
Writing a Polyfill for map in JavaScript
Does map mutate the original array in JavaScript?
More FAQs in Writing a Polyfill for map in JavaScript
Add a method to Array.prototype that loops through the array, calls the callback with (element, index, array), pushes the result to a new array, and returns the new array. Use let in the loop and do not mutate the original.
Three arguments: the current element, the current index, and the array itself. Most callbacks only use the first one, but the polyfill should pass all three to match the spec.
An optional second argument that sets this inside the callback. Support it with callback.call(thisArg, element, index, array) instead of callback(element, index, array).
Still have questions?
Browse all our FAQs or reach out to our support team
Want to upskill yourself?
Your learning library
Small steps. Big possibilities.
Find your next course. Build something great.