Group data with arrays and objects
Store ordered lists in arrays and describe things with object properties.
- Create and index an array
- Loop through array values
- Read properties from an object
An array stores an ordered list. Its first item is at index 0. An object groups named properties that describe one thing.
1const student = {
2 name: "Ada",
3 scores: [90, 100, 95],
4};
5
6console.log(student.name);
7console.log(student.scores[0]);Ada 90
Use a dot to read a property such as student.name, and square brackets with an index to read an array item such as scores[0]. Arrays also have useful methods like map, filter and reduce.
Key takeaways
Arrays are ordered and start at index 0.
Objects store named properties.
Use dot notation for a property and brackets for an index.
Lesson quiz
5 questions · pass with 4 correct · up to 50 XP
Passing this quiz completes the lesson and keeps your streak going. Questions you miss come back in review sessions later.
Practice: write JavaScript
Write the program, run it against the test cases, and use the feedback to build your JavaScript skills.
Student summary
The input is JSON for a student with a name and a scores array. Print the name, a colon, and the average score.
- Three scores
- Two scores
JavaScript runs in a sandboxed browser frame with a 1.5 second time limit. Input is available as the string variable input.
Questions about this lesson
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