How do you write 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.
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More FAQs in Writing a Polyfill for map in JavaScript
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.
No. map returns a new array with the results. The original array is unchanged. A polyfill should also not mutate the original array.
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).
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