String manipulation types (Uppercase, Lowercase) in Typescript

Introduction

Changing text to uppercase or lowercase helps make words look consistent or easier to compare.

When you want to make all letters in a name capital to show importance.

When you need to check if two words are the same without caring about big or small letters.

When you want to show a message in all small letters for style.

When sorting words and you want to ignore letter case differences.

Syntax

Typescript

string.toUpperCase()
string.toLowerCase()

These methods do not change the original string but return a new one.

They work on any string value.

Examples

This example shows how to get uppercase and lowercase versions of a word.

Typescript

const name = "hello";
const upper = name.toUpperCase();
const lower = name.toLowerCase();

Directly changing the case of a string inside console.log.

Typescript

console.log("TypeScript".toUpperCase());
console.log("TypeScript".toLowerCase());

Sample Program

This program changes a greeting to all uppercase and all lowercase, then prints both.

Typescript

const greeting = "Good Morning";

const shout = greeting.toUpperCase();
const whisper = greeting.toLowerCase();

console.log(shout);
console.log(whisper);

Important Notes

Remember, strings in TypeScript are not changed by these methods; you get new strings instead.

Use these methods to make text comparisons easier by standardizing letter case.

Summary

Use toUpperCase() to make all letters big.

Use toLowerCase() to make all letters small.

These methods help keep text consistent or easy to compare.

Practice

1. Which TypeScript string method converts all characters in a string to uppercase?

easy

A. convertCase()

B. toLowerCase()

C. toTitleCase()

D. toUpperCase()

Solution

1. Step 1: Understand string case methods

   TypeScript strings have built-in methods to change letter cases, including toUpperCase() and toLowerCase().

2. Step 2: Identify method for uppercase

   The method toUpperCase() changes all letters to uppercase, while toLowerCase() changes to lowercase.

3. Final Answer:

   toUpperCase() -> Option D

4. Quick Check:

   Uppercase method = toUpperCase() [OK]

Hint: Uppercase method always has 'Upper' in its name [OK]

Common Mistakes:

• Confusing toUpperCase() with toLowerCase()
• Thinking toTitleCase() exists in TypeScript
• Assuming convertCase() is a valid method

2. Which of the following is the correct syntax to convert a string variable name to lowercase in TypeScript?

easy

A. name.toLowerCase()

B. toLowerCase(name)

C. name.lowercase()

D. lowerCase(name)

Solution

1. Step 1: Recall method call syntax on strings

   In TypeScript, string methods are called on the string variable using dot notation.

2. Step 2: Identify correct method name and usage

   The method to convert to lowercase is toLowerCase(), called as name.toLowerCase(). Other options are invalid syntax or incorrect method names.

3. Final Answer:

   name.toLowerCase() -> Option A

4. Quick Check:

   Lowercase method called on variable = name.toLowerCase() [OK]

Hint: String methods use dot notation like variable.method() [OK]

Common Mistakes:

• Using function style like toLowerCase(name)
• Using incorrect method names like lowercase()
• Missing parentheses after method name

3. What will be the output of the following TypeScript code?

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

medium

A. "hello world"

B. SyntaxError

C. "HELLO WORLD"

D. "Hello World"

Solution

1. Step 1: Understand the input string and method

   The string is "Hello World" and the method toUpperCase() converts all letters to uppercase.

2. Step 2: Apply toUpperCase() to the string

   Applying toUpperCase() changes "Hello World" to "HELLO WORLD".

3. Final Answer:

   "HELLO WORLD" -> Option C

4. Quick Check:

   toUpperCase() output = "HELLO WORLD" [OK]

Hint: toUpperCase() makes all letters big exactly [OK]

Common Mistakes:

• Expecting lowercase output instead
• Thinking original string is unchanged in output
• Confusing method name causing syntax error

4. Identify the error in this TypeScript code snippet:

let greeting = "Hi There";
console.log(greeting.toLowercase());

medium

A. Missing semicolon after string declaration

B. toLowercase() is not a valid method; correct is toLowerCase()

C. Variable greeting should be const, not let

D. Console.log should be console.Log

Solution

1. Step 1: Check method name spelling

   The method to convert string to lowercase is toLowerCase() with capital 'C'. The code uses toLowercase() with lowercase 'c', which is invalid.

2. Step 2: Verify other syntax elements

   Semicolon is optional in TypeScript, let is valid for variable, and console.log is case-sensitive and correct as written.

3. Final Answer:

   toLowercase() is not a valid method; correct is toLowerCase() -> Option B

4. Quick Check:

   Method name case matters: toLowerCase() correct [OK]

Hint: Method names are case-sensitive; watch capital letters [OK]

Common Mistakes:

• Ignoring case sensitivity in method names
• Thinking semicolon is mandatory error
• Confusing console.log capitalization

5. You have an array of strings: const fruits = ["Apple", "BANANA", "Cherry"];
How do you create a new array where all fruit names are lowercase using TypeScript?

hard

A. fruits.map(fruit => fruit.toLowerCase())

B. fruits.toLowerCase()

C. fruits.forEach(fruit => fruit.toLowerCase())

D. fruits.map(fruit => toLowerCase(fruit))

Solution

1. Step 1: Understand array transformation

   To change each string in an array, use map() to create a new array with transformed values.

2. Step 2: Apply toLowerCase() inside map callback

   Inside map, call fruit.toLowerCase() to convert each string to lowercase. This returns a new array with all lowercase fruits.

3. Final Answer:

   fruits.map(fruit => fruit.toLowerCase()) -> Option A

4. Quick Check:

   Use map() with toLowerCase() for array lowercase [OK]

Hint: Use map() with toLowerCase() to transform arrays [OK]

Common Mistakes:

• Calling toLowerCase() directly on array
• Using forEach which returns void, not new array
• Trying to call toLowerCase() as a standalone function