Total an array with reduce

Read first Task 52

`reduce` walks an array and carries one running value. It is the cleanest way to add up a column of numbers.

Definition and example

Total an array with reduce is the focus of this lesson. `reduce` walks an array and carries one running value. It is the cleanest way to add up a column of numbers. The task asks you to apply that idea in a small example: Task: Total an array with reduce. What does this program print. Before you run the code, predict what should happen. Then Inspect the browser output and the value your code produces and compare it with your prediction. If the result differs, change one relevant line and run it again. Testing one change at a time makes the cause of a result easier to understand.

JavaScript 1 automatic check Capstone: real browser patterns

Code editor Ctrl + Enter runs

// TASK total-an-array-with-reduce-02: Task: Total an array with reduce. What does this program print?
// STEPS: Read the explanation. Change one relevant line at a time, then run the code and compare the result with the check on the right.
const marks = [850, 920, 780, 640];

const total = marks.reduce((sum, mark) => sum + mark, 0);
const average = total / marks.length;

console.log('Total:', total);
console.log('Average:', average);

Run your code to see the output and the checks.

Your result

Submit your code to see results

Write your code in the middle column and press Run code.

Checks on this task:

The output must include “Average: 797.5”.

The task and step-by-step instructions are written as comments at the top of the editor. Change one relevant line, run it, and compare the result with these checks.

Incorrect attempts before answer: 0 / 3

Track progress

0 passed of 56 tasks

Pass every check or use one of your available skips to open the next task.

← Previous

Next task (pass every check first)

Total an array with reduce

Total an array with reduce

Why this works