TypeScript Strings

Strings are a basic data type used to represent text data. In TypeScript, the type of strings is string. You can use single quotes ('), double quotes ("), or backticks (`) to create strings.

Creating Strings

let singleQuote: string = 'Hello';
let doubleQuote: string = "World";

Template Strings

Template strings are a feature introduced in ES6, using backticks (`). They provide more powerful functionality:

1. Embedding expressions: You can embed variables or any valid JavaScript expression in strings using ${expression} syntax.
2. Multi-line strings: Strings can span multiple lines without needing to use + or \.

Example

let name: string = "TypeScript";
let version: number = 5.2;

// Embedding variables
let greeting: string = `Hello, ${name}!`;
console.log(greeting); // Output: Hello, TypeScript!

// Embedding expressions
let message: string = `The next version will be ${version + 0.1}.`;
console.log(message); // Output: The next version will be 5.3.

// Multi-line strings
let multiLine: string = `
This is a string
that spans across
multiple lines.
`;
console.log(multiLine);

Common String Properties and Methods

TypeScript strings have the same properties and methods as JavaScript strings.

length Property

Returns the length of the string.

let str = "Hello, World!";
console.log(str.length); // 13

Common Methods

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

  console.log(str.charAt(0)); // 'H'

• concat(...strings): Concatenates one or more strings and returns a new string.

  let str1 = "Hello";
  let str2 = " World";
  console.log(str1.concat(str2, "!")); // "Hello World!"

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

  console.log(str.indexOf('o')); // 4
  console.log(str.indexOf('z')); // -1

• slice(startIndex, endIndex): Extracts a section of a string and returns a new string. endIndex is optional.

  console.log(str.slice(0, 5)); // "Hello"
  console.log(str.slice(7)); // "World!"

• split(separator): Splits a string into an array of strings using the specified separator.

  let words = str.split(' ');
  console.log(words); // ["Hello,", "World!"]

• toLowerCase(): Converts the string to lowercase.

  console.log(str.toLowerCase()); // "hello, world!"

• toUpperCase(): Converts the string to uppercase.

  console.log(str.toUpperCase()); // "HELLO, WORLD!"

• trim(): Removes whitespace from both ends of the string.

  let paddedStr = "   some text   ";
  console.log(paddedStr.trim()); // "some text"

• substring(startIndex, endIndex): Returns the substring between the specified indexes.

  console.log(str.substring(0, 5)); // "Hello"

Thanks to TypeScript's type system, when you call these methods, IDEs (like VS Code) can provide intelligent auto-completion and parameter information hints, greatly improving development efficiency.