Storing objects in an array

Name:

Date:

Class:

Quick Questions

Shade in the A or B circle for each question.

1. Which line creates a new Student object and adds it to the end of the students array?

A students.push(Student('Ava', 7));

B students.push(new Student('Ava', 7));

2. After these lines run, how many objects are in the array? let students = []; students.push(new Student('Ava', 7)); students.push(new Student('Liam', 8));

A 2

B 0

3. Which loop visits every Student object in the students array and calls its method?

A for (const s of students) { s.introduce(); }

B for (const s of Student) { s.introduce(); }

4. Inside a for...of loop with 'const s of students', how do you read one student's points?

A s.points

B students.points

5. You want the total of every student's points. Which is correct?

A let total = 0; for (const s of students) { total = s.points; }

B let total = 0; for (const s of students) { total += s.points; }

Match the Pairs

Draw a line connecting each item on the left to its match on the right.

Left column		Right column
1students.push(new Student('Ava', 7));		Afor (const s of students) { if (s.name === 'Ava') { found = s; } }
2for (const s of students) { s.greet(); }		BCreates a new Student object and adds it to the end of the students array
3To find the total of one property across all objects in an array, add it up inside a loop		CVisits each Student object in the array and calls its greet() method
4To find an object by a property, loop through the array and check each object's property		DIt reads points from the whole array instead of the current object. It should be total += s.points;
5students.push(Student('Ava', 7));		EThe new keyword is missing, so Student is called like a normal function and no object is created. It should be students.push(new Student('Ava', 7));
6for (const s of students) { total += students.points; }		Flet total = 0; for (const s of students) { total += s.points; }

Definitions

students.push(new Student('Ava', 7));

Fill in the Blanks

Complete each line of code by filling in the missing parts.

students.____(new Student('Ava', 7));

for (const s __ students) { s.greet(); }

for (const s of students) { if (s.name ___ 'Ava') found = s; }

let total = 0; for (const s of students) total __ s.points;

const students = []; students.push(___ Student('Liam', 8));

Spot the Error

Shade in the letter of the line that contains an error.

Question 1

A const list = [];

B list.push(new Student("Ava"));

C list.push(Student("Zoe"));

D console.log(list.length);

Question 2

A let total = 0;

B for (const s in list) {

C total += s.points;

D }

E console.log(total);

Question 3

A const list = {};

B list.push(new Student("Ava"));

C list.push(new Student("Zoe"));

D console.log(list.length);

Question 4

A let found = null;

B for (const s of list) {

C if (s.name === "Zoe") {

D found == s;

E }

F }

Question 5

A const list = [];

B list.add(new Student("Ava"));

C for (const s of list) {

D s.sayHi();

E }

Answer Key

Storing objects in an array

Section A: Quick Questions

B — students.push(new Student('Ava', 7));

A — 2

A — for (const s of students) { s.introduce(); }

A — s.points

B — let total = 0; for (const s of students) { total += s.points; }

Section B: Match the Pairs

students.push(new Student('Ava', 7)); → Creates a new Student object and adds it to the end of the students array

for (const s of students) { s.greet(); } → Visits each Student object in the array and calls its greet() method

To find the total of one property across all objects in an array, add it up inside a loop → let total = 0; for (const s of students) { total += s.points; }

To find an object by a property, loop through the array and check each object's property → for (const s of students) { if (s.name === 'Ava') { found = s; } }

students.push(Student('Ava', 7)); → The new keyword is missing, so Student is called like a normal function and no object is created. It should be students.push(new Student('Ava', 7));

for (const s of students) { total += students.points; } → It reads points from the whole array instead of the current object. It should be total += s.points;

Section C: Definitions

students.push(new Student('Ava', 7)); — Makes a new Student object and adds it to the end of the students array. You can then loop over the array and call each object's methods.

Section D: Fill in the Blanks

students.push(new Student('Ava', 7));

for (const s of students) {
  s.greet();
}

for (const s of students) {
  if (s.name === 'Ava') found = s;
}

let total = 0;
for (const s of students) total += s.points;

const students = [];
students.push(new Student('Liam', 8));

Section E: Spot the Error

C — Student is a class, so you must use the new keyword to make an object before pushing it. It should be list.push(new Student("Zoe"));

B — for...in gives the index positions ("0", "1"...), not the Student objects, so s.points is undefined and the total becomes NaN. Use for...of to visit each object.

A — {} makes an object, which has no push method, so list.push causes a TypeError. An array of Students must be created with [] instead.

D — == compares values instead of storing one. found would stay null. Use a single = to assign the matching Student: found = s;

B — Arrays do not have an add method. To put a new object on the end of an array, use push: list.push(new Student("Ava"));