Which array method reduces an array to a single value using a reducer function?

Which array method reduces an array to a single value using a reducer function?

• A. Reduce
• B. Map
• C. Filter
• D. Find

Answer: (A)

Reducing an array to a single value means you carry along a running result as you move through each element, updating that result with a reducer function. The function takes two main things: an accumulator (the running total or current result) and the current element from the array. It returns the new accumulator. You can also provide an initial value for the accumulator; if you do, that value starts the process. If you don’t provide one, the first element of the array becomes the initial accumulator and the iteration starts with the second element.

For example, to sum numbers in an array, you’d use a reducer that adds the current element to the accumulator: [1, 2, 3, 4].reduce((acc, cur) => acc + cur, 0) yields 10. Different kinds of reductions are possible: you can build a single number, a string, an object, or even a more complex data structure by carefully returning the new accumulator from the reducer.

This method differs from other array tools. Mapping creates a new array by applying a function to every element, leaving you with the same-length array. Filtering selects elements that pass a condition, resulting in a potentially smaller array. Finding returns the first element that matches a condition, not a cumulative result across the whole array. The reducer approach is specifically about combining all elements into one final value.