String Search Methods

Checks whether a string contains a given substring, returning true or false.

Part of: JavaScript Coding without HTML and CSS — Module 31

Understanding String Search Methods in JavaScript

What it does: indexOf() returns -1 when the substring doesn't appear. This tests whether "cat" appears anywhere inside word. includes() checks for a substring and returns a boolean result. indexOf() returns a position number, not true or false. JavaScript uses camelCase, so it must be indexOf. Both includes() and indexOf() need a value to search for. JavaScript is case-sensitive, so it must be lowercase 'includes'. includes() is used to test whether a substring exists.

Common mistakes: 'includes' must be lowercase - a capital I causes an error. Method names are camelCase - it should be indexOf, not indexof.

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Free printable worksheet with full answer key — or add this module to a class and your students practise it interactively.

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This module's key terms are also in a printable crossword (Modules 31–40) and word search (Modules 21–52).

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Learning

Duo

Does includes() return true or false?

YesNo

Matches

text.Includes("world")

↓

Wrong - 'includes' must start with a lowercase i

Applying

Meanings

Term

includes()

Meaning

Checks whether a string contains a given substring, returning true or false.

Practice

let text = "hello world";

Testing

Gaps

console.log(text.("world"));

Check Answer

Spots

1let a = "hi there";

2console.log(a.Includes("hi"));

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Quick Questions

1. Does includes() return true or false?

A. Yes ✓

B. No

includes() checks for a substring and returns a boolean result.

2. Does indexOf() return a boolean like includes() does?

A. Yes

B. No ✓

indexOf() returns a position number, not true or false.

3. Does indexOf() return -1 when the substring isn't found?

A. Yes ✓

B. No

-1 signals that the substring doesn't appear in the string.

4. Is 'indexof' with a lowercase o valid JavaScript syntax?

A. Yes

B. No ✓

JavaScript uses camelCase, so it must be indexOf.

5. Do these search methods need a substring passed as an argument?

A. Yes ✓

B. No

Both includes() and indexOf() need a value to search for.

Match the Pairs

text.includes("world") → Returns true if text contains "world"

text.indexOf("world") → Returns the position where "world" starts in text

The value returned when a substring isn't found → -1

Checks whether a substring exists in a string → word.includes("cat")

text.Includes("world") → Wrong - 'includes' must start with a lowercase i

text.indexof("world") → Wrong - method names are camelCase: indexOf

Key Term

includes()

Checks whether a string contains a given substring, returning true or false.

Fill in the Blanks

1. console.log(text.includes("world"));

Hint: Type the method that checks if a string contains a substring.

2. console.log(text.indexOf("world"));

Hint: Type the method that returns the position of a substring.

3. let found = word.includes("cat");

Hint: Type the method that checks if a string contains a substring.

4. let pos = word.indexOf("cat");

Hint: Type the method that returns the position of a substring.

5. let hasDog = text.includes("dog");

Hint: Type the method that checks if a string contains a substring.

Spot the Error

Question 1

A let a = "hi there";

B console.log(a.Includes("hi"));

C console.log(a);

Line B — 'includes' must be lowercase - a capital I causes an error.

Question 2

A let b = "good day";

B console.log(b);

C console.log(b.indexof("day"));

Line C — Method names are camelCase - it should be indexOf, not indexof.

Question 3

A let c = "hi there";

B console.log(c);

C console.log(c.includes);

Line C — Missing parentheses and the search value - includes() needs an argument.

Question 4

A console.log(d.indexOf);

B let d = "good day";

C console.log(d);

Line A — Missing parentheses and the search value - indexOf() needs an argument.

Question 5

A let e = "hi there";

B console.log(e.includes("hi"));

C console.log(e);

D console.log(e.Includes("hi"));

Line D — 'includes' must be lowercase - a capital I causes an error.

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