throw Statement

Creates a custom error and immediately stops the current code from running further.

Part of: JavaScript Coding without HTML and CSS — Module 45, ACARA Digital Technologies Years 9–10 — Modular and Object-Oriented Programming (JavaScript) — Module 43

Understanding throw Statement in JavaScript

What it does: throw is exactly the keyword that does this. A thrown error inside try can be handled by catch. throw raises an error that can be handled elsewhere. Execution stops immediately at the point throw is called. JavaScript is case-sensitive, so 'throw' must be lowercase. Error is a built-in object and must be capitalized. The correct spelling is 'throw', not 'trow'. throw can raise any value, including a plain string.

Common mistakes: 'throw' must be lowercase - a capital T causes an error. 'Error' must start with a capital E, not lowercase.

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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 41–52) and word search (Modules 21–52).

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Each concept is reinforced from every angle — learned, then applied, then tested.

Learning

Duo

Does throw create a custom error?

YesNo

Matches

Throw new Error("Bad");

↓

Wrong - 'throw' must be lowercase

Applying

Meanings

Term

throw

Meaning

Creates a custom error and immediately stops the current code from running further.

Practice

try {

Testing

Gaps

new Error("Something broke");

Check Answer

Spots

1Throw new Error("Bad");

2console.log("after");

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Quick Questions

1. Does throw create a custom error?

A. Yes ✓

B. No

throw raises an error that can be handled elsewhere.

2. Does throw stop the current code from running further?

A. No

B. Yes ✓

Execution stops immediately at the point throw is called.

3. Can a thrown error be caught by a catch block?

A. Yes ✓

B. No

If throw happens inside try, catch can handle the error.

4. Must 'throw' be written in lowercase?

A. No

B. Yes ✓

JavaScript is case-sensitive, so 'throw' must be lowercase.

5. Must 'Error' start with a capital E when using new Error()?

A. Yes ✓

B. No

Error is a built-in object and must be capitalized.

Match the Pairs

throw new Error("Something broke"); → Raises a custom error and stops execution at that point

throw new Error("Bad age"); → Raises an error describing an invalid age

Creates and raises a custom error → throw

Can be caught by a matching catch block → try { throw new Error("X"); } catch (e) { ... }

Throw new Error("Bad"); → Wrong - 'throw' must be lowercase

throw new error("Bad"); → Wrong - 'Error' must start with a capital E

Key Term

throw

Creates a custom error and immediately stops the current code from running further.

Fill in the Blanks

1. throw new Error("Something broke");

Hint: Type the keyword that raises a custom error.

2. throw new Error("Invalid input");

Hint: Type the built-in type used to create an error.

3. throw new Error("No data found");

Hint: Type the keyword that raises a custom error.

4. if (age < 0) { throw new Error("Bad age"); }

Hint: Type the keyword that raises a custom error.

5. throw new Error("Out of range");

Hint: Type the built-in type used to create an error.

Spot the Error

Question 1

A Throw new Error("Bad");

B console.log("after");

C let x = 1;

Line A — 'throw' must be lowercase - a capital T causes an error.

Question 2

A throw new error("Bad");

B console.log("after");

C let x = 1;

Line A — 'Error' must start with a capital E, not lowercase.

Question 3

A let a = 1;

B throw "Bad";

C console.log(a);

Line B — This line is actually correct - throw can raise a plain string too.

Question 4

A let b = 2;

B trow new Error("Bad");

C console.log(b);

Line B — 'throw' is misspelled as 'trow'.

Question 5

A try {

B throw new Error("Oops");

C } catch (e) {

D console.log(e.message)

E }

Line D — This line is missing a semicolon, but that's not required in JS.

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