TypeScript Strings

last modified February 24, 2025

TypeScript strings store textual data as character sequences. They extend JavaScript strings with type annotations for better code safety. This guide explores declaration, manipulation methods, and practical use cases.

What Are TypeScript Strings?

Strings in TypeScript represent immutable sequences of Unicode characters. They can be declared with single quotes, double quotes, or template literals. Type annotations ensure only string values are assigned.

Creating Strings

This example shows different ways to declare TypeScript strings.

declaring_strings.ts

let greeting: string = "Welcome";
let filename: string = 'app.js';
let path: string = `C:/projects/${filename}`;

console.log(path);  // Output: C:/projects/app.js

Template literals (backticks) allow embedded expressions. All declarations create immutable string values with type safety.

String Methods

This example demonstrates essential string manipulation methods.

string_methods.ts

let message: string = "TypeScript Essentials";

console.log(message.charAt(4));     // Output: S
console.log(message.slice(4, 10));  // Output: Script
console.log(message.includes("Ess"));  // Output: true
console.log(message.replace("Essentials", "Mastery"));
// Output: TypeScript Mastery

Common methods include charAt for character access, slice for substring extraction, and replace for pattern substitution.

String Interpolation

This example shows how to use template literals for dynamic strings.

string_interpolation.ts

let user: string = "Alice";
let tasks: number = 5;

console.log(`${user} has ${tasks} pending tasks`);
// Output: Alice has 5 pending tasks

Template literals simplify string concatenation and support multi-line strings without escape characters.

String Validation

This example demonstrates basic string validation techniques.

string_validation.ts

function isValidEmail(email: string): boolean {
    return email.includes("@") && email.includes(".");
}

console.log(isValidEmail("user@example.com"));  // Output: true
console.log(isValidEmail("invalid.email"));     // Output: false

Basic validation checks can be implemented using includes and other string methods. For production, use regular expressions.

Iterating Over Strings

This example shows how to access individual characters in a string.

string_iteration.ts

let charset: string = "ABCD";

for (let char of charset) {
    console.log(char);
}
// Output:
// A
// B
// C
// D

The for...of loop iterates through each character. Strings are iterable in TypeScript/JavaScript.

Best Practices

Use Template Literals: Improve readability with embedded expressions
Prefer const: Declare fixed strings with const
Sanitize Inputs: Validate and trim user input strings
Use Methods Wisely: Choose between slice, substring based on needs
Handle Encoding: Consider Unicode characters in modern apps

Source

TypeScript String Documentation

This tutorial covered essential string operations in TypeScript, providing foundational knowledge for text processing in type-safe applications.

Author

My name is Jan Bodnar, and I am a passionate programmer with extensive programming experience. I have been writing programming articles since 2007. To date, I have authored over 1,400 articles and 8 e-books. I possess more than ten years of experience in teaching programming.

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