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Exercise 7

Use reduce to compute the sum of the squares of all of the numbers in an array:

let array = [3, 5, 7];
console.log(sumOfSquares(array)); // => 83

Note that 83 is 3*3 + 5*5 + 7*7.

Solution

function sumOfSquares(numbers) {
  return numbers.reduce((accumulator, number) => {
    return accumulator + number * number;
  }, 0);
}

let array = [3, 5, 7];
console.log(sumOfSquares(array)); // => 83

What happens if you forget to provide an initial value of 0 for the accumulator? Take a look at the MDN Documentation for reduce and see if you can determine what sumOfSquares would return if you omitted the initial accumulator value.

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