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Array Aggregation: The reduce() Method (Simple Use)

JavaScript: The Complete '0 to Hero' Beginner Course

61. Array Aggregation: The .reduce() Method

.reduce() is the most versatile array method. It executes a callback function on every element of the array, resulting in a single output value (the 'accumulator'). This is useful for summarizing, counting, or summing data.

Syntax

javascript array.reduce(callback(accumulator, currentValue), initialValue);

  • Accumulator: The running total (the result of the previous calculation).
  • Current Value: The element currently being processed.
  • Initial Value: The starting value for the accumulator (optional, but highly recommended).

Example: Calculating a Total Sum

javascript const numbers = [10, 5, 2];

const sum = numbers.reduce((total, number) => { console.log(Accumulator: ${total}, Current: ${number}); return total + number; }, 0); // Start the total at 0

console.log('Final Sum:', sum); // Output: Final Sum: 17

Note: .reduce() can also be used to transform an array into an object, which we will cover in a more advanced lesson.