Searching an array with includes and indexOf
Name:
Date:
Class:
A
Quick Questions
Shade in the A or B circle for each question.
1. Which line checks if "Ava" is in the array names and gives true or false?
2. let pets = ["cat", "dog"];
What does pets.includes("fish") give?
3. let nums = [5, 8, 12];
What does nums.indexOf(12) give?
4. let colours = ["red", "blue"];
What does colours.indexOf("green") give?
5. Which if statement correctly checks that "Leo" is NOT in the array team?
B
Match the Pairs
Draw a line connecting each item on the left to its match on the right.
| Left column | Right column | |
|---|---|---|
| 1fruits.includes("apple") | A0 is the position of the first item, not a 'not found' result. Not found is -1, so this misses red at other positions. Use !== -1 to check it was found. | |
| 2fruits.indexOf("pear") | BGives true if "apple" is in the fruits array, otherwise false | |
| 3Use includes inside an if to run code only when a value is in the array | Cif (names.includes("Zoe")) { console.log("Found"); } | |
| 4Check that indexOf did not find the value by comparing the result with -1 | DGives the position of "pear" in the array, or -1 if it is not found | |
| 5if (colours.indexOf("red") === 0) { console.log("Found"); } | Eif (scores.indexOf(50) === -1) { console.log("Not found"); } | |
| 6let pos = fruits.includes("kiwi"); | Fincludes gives true or false, not a position. To get the position of kiwi you need indexOf. |
C
Definitions
includes(value)
D
Fill in the Blanks
Complete each line of code by filling in the missing parts.
1.
const pets = ["cat", "dog", "fish"];
console.log(pets.________("dog"));
2.
const names = ["Ava", "Liam", "Mia"];
console.log(names._______("Mia"));
3.
const scores = [70, 85, 92];
console.log(scores.indexOf(50) === __);
4.
const games = ["chess", "tag"];
if (games.________("tag"))
console.log("Found!");
5.
const colours = ["red", "blue"];
if (_colours.includes("green"))
console.log("Not found");
E
Spot the Error
Shade in the letter of the line that contains an error.
Question 1
A
const n = ["Ava", "Leo"];
B
const i = n.indexOf("Zed");
C
console.log(i);
D
console.log(i === 0);
Question 2
A
const n = [4, 8, 15];
B
console.log(n.include(8));
C
console.log(n.indexOf(8));
Question 3
A
const t = ["a", "b", "c"];
B
const pos = t.indexOf("b");
C
if (pos === -1) {
D
console.log("At", pos);
E
}
Question 4
A
const f = ["pie", "tea"];
B
const has = f.includes("tea");
C
if (has === "true") {
D
console.log("Yes");
E
}
Question 5
A
const pets = {"cat", "dog"};
B
const i = pets.indexOf("dog");
C
console.log(i);
Answer Key
Searching an array with includes and indexOf
Section A: Quick Questions
Q1
A — names.includes("Ava")
Q2
B — false
Q3
A — 2
Q4
A — -1
Q5
B — if (team.indexOf("Leo") === -1)
Section B: Match the Pairs
Q1
fruits.includes("apple") → Gives true if "apple" is in the fruits array, otherwise false
Q2
fruits.indexOf("pear") → Gives the position of "pear" in the array, or -1 if it is not found
Q3
Use includes inside an if to run code only when a value is in the array → if (names.includes("Zoe")) { console.log("Found"); }
Q4
Check that indexOf did not find the value by comparing the result with -1 → if (scores.indexOf(50) === -1) { console.log("Not found"); }
Q5
if (colours.indexOf("red") === 0) { console.log("Found"); } → 0 is the position of the first item, not a 'not found' result. Not found is -1, so this misses red at other positions. Use !== -1 to check it was found.
Q6
let pos = fruits.includes("kiwi"); → includes gives true or false, not a position. To get the position of kiwi you need indexOf.
Section C: Definitions
Q1
includes(value) — Array method that gives true if the value is in the array, otherwise false. Its partner indexOf(value) gives the position, or -1 if the value is not found.Section D: Fill in the Blanks
Q1
const pets = ["cat", "dog", "fish"];
console.log(pets.includes("dog"));Q2
const names = ["Ava", "Liam", "Mia"];
console.log(names.indexOf("Mia"));Q3
const scores = [70, 85, 92];
console.log(scores.indexOf(50) === -1);Q4
const games = ["chess", "tag"];
if (games.includes("tag"))
console.log("Found!");Q5
const colours = ["red", "blue"];
if (!colours.includes("green"))
console.log("Not found");Section E: Spot the Error
Q1
D — indexOf gives -1 when the value is not found, not 0 (0 is the first position). The check should be i === -1.
Q2
B — The method is called includes, with an s on the end. include is not an array method and causes a TypeError.
Q3
C — The condition is backwards. The code inside should run when the value IS found, so it must be pos !== -1.
Q4
C — includes gives the boolean true, not the string "true", so this comparison is never true. Use if (has) {.
Q5
A — An array is written with square brackets, not curly braces. It should be const pets = ["cat", "dog"];