String manipulation types (Uppercase, Lowercase) in Typescript - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

What is the output of this TypeScript code?

Consider this code snippet that changes the case of a string:

const greeting = "Hello World";
const result = greeting.toUpperCase();
console.log(result);

What will be printed to the console?

Typescript

const greeting = "Hello World";
const result = greeting.toUpperCase();
console.log(result);

A "HELLO WORLD"

B "hello world"

C "Hello World"

D "HeLLo WoRLD"

💡 Hint

Think about what toUpperCase() does to each letter.

The toUpperCase() method converts all letters in the string to uppercase. So "Hello World" becomes "HELLO WORLD".

❓ Predict Output

intermediate

What is the output of this TypeScript code?

Look at this code that changes string case:

const text = "TypeScript";
const lower = text.toLowerCase();
console.log(lower);

What will be printed to the console?

Typescript

const text = "TypeScript";
const lower = text.toLowerCase();
console.log(lower);

A "TYPESCRIPT"

B "typescript"

C "TypeScript"

D "TyPeScRiPt"

💡 Hint

Remember what toLowerCase() does.

The toLowerCase() method converts all letters in the string to lowercase. So "TypeScript" becomes "typescript".

❓ Predict Output

advanced

What is the output of this TypeScript code with mixed case methods?

Check this code that uses both uppercase and lowercase methods:

const phrase = "JavaScript Rocks!";
const part1 = phrase.substring(0, 10).toLowerCase();
const part2 = phrase.substring(10).toUpperCase();
console.log(part1 + part2);

What will be printed to the console?

Typescript

const phrase = "JavaScript Rocks!";
const part1 = phrase.substring(0, 10).toLowerCase();
const part2 = phrase.substring(10).toUpperCase();
console.log(part1 + part2);

A "javascript ROCKS!"

B "JAVASCRIPT rocks!"

C "javascript rocks!"

D "JavaScript ROCKS!"

💡 Hint

Look carefully at how substring and case methods combine.

The first 10 characters "JavaScript" become lowercase "javascript". The substring from index 10 is " Rocks!" which becomes uppercase " ROCKS!". Concatenated, it prints "javascript ROCKS!".

❓ Predict Output

advanced

What is the output of this TypeScript code using chaining?

Observe this code that chains string methods:

const input = "  Mixed CASE String  ";
const output = input.trim().toLowerCase().replace(/ /g, "_");
console.log(output);

What will be printed to the console?

Typescript

const input = "  Mixed CASE String  ";
const output = input.trim().toLowerCase().replace(/ /g, "_");
console.log(output);

A "Mixed_CASE_String"

B "MIXED_CASE_STRING"

C "mixed_case_string"

D "mixed CASE String"

💡 Hint

Think about what each method does step by step.

trim() removes spaces at start and end, toLowerCase() makes all letters lowercase, and replace(/ /g, "_") replaces all spaces with underscores. Result is "mixed_case_string".

🧠 Conceptual

expert

Which option will cause a runtime error in TypeScript when manipulating string cases?

Consider these four code snippets. Only one will cause a runtime error when run. Which one is it?

A

const s: string = "hello";
console.log(s.toLowerCase());

B

const s: string | undefined = undefined;
console.log(s?.toLowerCase());

C

const s: string | null = null;
console.log(s?.toUpperCase());

D

const s: any = 123;
console.log(s.toUpperCase());

💡 Hint

Think about what happens if you call a string method on a non-string value.

Option D assigns a number to s and calls toUpperCase() on it. Numbers do not have this method, so it causes a runtime error. Other options safely handle null, undefined, or valid strings.