The String Type in TypeScript

In TypeScript, the string type is used to represent sequences of characters. Strings can be defined using single quotes ('), double quotes ("), or backticks (`) for template strings.

let message: string = "Hello, TypeScript!";
let greeting: string = 'Welcome!';
let template: string = `This is a TypeScript message`;

Template Strings

Template strings allow embedding expressions, making it easier to construct complex strings. They are delimited by backticks (`) and can contain interpolated expressions using ${}.

let name: string = "John";
let age: number = 30;
let message: string = `Hello, my name is ${name} and I am ${age} years old.`;
console.log(message);  // "Hello, my name is John and I am 30 years old."

Escaping Characters

To include special characters in a string, escape sequences are used.

• \n: New line
• \t: Tab
• \\: Backslash
• \': Single quote
• \": Double quote

let multiline: string = "Line 1\nLine 2";
console.log(multiline);
// Line 1
// Line 2

String Concatenation

String concatenation can be done using the + operator or the concat method and template strings.

Using the + Operator

let greeting: string = "Hello, " + name + ". Welcome to " + text + "!";
console.log(greeting);  // "Hello, John. Welcome to TypeScript!"

Using concat

let concatenatedGreeting: string = greeting.concat(" Enjoy your learning!");
console.log(concatenatedGreeting);  // "Hello, John. Welcome to TypeScript! Enjoy your learning!"

Using Template Strings

let templateGreeting: string = `Hello, ${name}. Welcome to ${text}!`;
console.log(templateGreeting);  // "Hello, John. Welcome to TypeScript!"

String Comparison

Strings can be compared using comparison operators (<, >, <=, >=, ==, !=, ===, !==). Comparisons are case-sensitive.

let string1: string = "abc";
let string2: string = "Abc";

console.log(string1 === string2);  // false
console.log(string1.toLowerCase() === string2.toLowerCase());  // true

String Methods and Properties

TypeScript provides a variety of methods and properties to manipulate strings. Let’s look at some of the most commonly used.

• length: Returns the length of the string.

let text: string = "TypeScript";
console.log(text.length);  // 10

• charAt(index): Returns the character at the specified position.

console.log(text.charAt(0));  // "T"

• concat(...strings): Combines two or more strings.

let part1: string = "Hello, ";
let part2: string = "TypeScript";
console.log(part1.concat(part2));  // "Hello, TypeScript"

• includes(substring): Checks if a string contains another string.

console.log(text.includes("Script"));  // true

• indexOf(substring): Returns the index of the first occurrence of a substring, or -1 if not found.

console.log(text.indexOf("Script"));  // 4

• replace(substring, newString): Replaces a substring with another.

console.log(text.replace("Type", "Java"));  // "JavaScript"

• split(separator): Splits a string into an array of substrings.

let list: string = "apple,banana,pear";
console.log(list.split(","));  // ["apple", "banana", "pear"]

• substring(start, end): Returns a substring from the start index to the end index (not inclusive).

console.log(text.substring(0, 4));  // "Type"

• toLowerCase(): Converts all characters in a string to lowercase.

console.log(text.toLowerCase());  // "typescript"

• toUpperCase(): Converts all characters in a string to uppercase.

console.log(text.toUpperCase());  // "TYPESCRIPT"