map and filter

JavaScript · Unit 5: Arrays

map creates a new array: you hand it a function and it stores whatever that function returns with each item.

const nums = [10, 20, 30];
const doubles = nums.map(
  (n) => n * 2
);
console.log(doubles);

Prints

[ 20, 40, 60 ]

The rest of the explanation is in the lesson, which is part of the full plan.

Exercises in this lesson

You do them in the app, which checks them on the spot and explains why.

1. Predict the output
What does this code print?
2. Complete the code
Complete it to turn the pounds into ounces.
3. Multiple choice
Which line does the same as this loop?
4. Predict the output
What does this code print?
5. Predict the output
What does this code print?
6. Complete the code
Complete it to keep the failing scores (under 60).
7. Multiple choice
You have the prices and you want the ones over 100, without changing anything. What do you use?
8. Find the bug
This program should print the doubles. Which line has the error?
9. Put the lines in order
Put in order the function that returns only the passing scores (60 or more).
10. Predict the output
These are Mia's scores. What does it print?

It opens in your browser. This lesson is part of the full plan; the first unit of each course is free.