TypeScript Variables
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TypeScript Variables
TypeScript is a statically typed language that allows developers to define variables with a specific type. In this lesson, we will learn how to declare variables in TypeScript and explore the different types available.
Declaring Variables in TypeScript
To declare a variable in TypeScript, we use the let
or const
keyword, followed by the variable name and an optional type annotation:
let message: string = "Hello, TypeScript!"; const pi: number = 3.14;
The let
keyword is used for variables that can be reassigned, while the const
keyword is used for variables that are read-only and cannot be reassigned.
Types of Variables in TypeScript
TypeScript provides several types of variables, including:
number
: A numeric value, including integers and floating-point numbers.string
: A sequence of characters that represent text.boolean
: A value that can be eithertrue
orfalse
.array
: A collection of values of the same type.tuple
: An array with a fixed number of elements, where each element may have a different type.enum
: A way to define a set of named constants.any
: A type that represents any value.void
: A type that indicates the absence of a value.
Examples
let age: number = 30; let name: string = "John Doe"; let isStudent: boolean = true; let grades: number[] = [90, 85, 95]; let contact: [string, number] = ["John Doe", 1234567890]; enum Color {Red, Green, Blue}; let color: Color = Color.Red; let anyValue: any = "Hello World!"; let nothing: void = undefined;
FAQs
Q: Can I declare a variable without a type annotation in TypeScript?
A: Yes, you can declare a variable without a type annotation, and TypeScript will automatically infer the type based on the value assigned to the variable.
Q: Can I declare a variable with a different type than the one initially assigned to it?
A: No, once you declare a variable with a specific type, you cannot assign a value of a different type to it.
Q: Can I declare a variable as undefined
in TypeScript?
A: Yes, you can declare a variable as undefined
by assigning it the value undefined
or by omitting the value assignment. However, it is recommended to use the null
type instead of undefined
to indicate the absence of a value.
Q: What is the difference between null
and undefined
in TypeScript?
A: null
and undefined
are both used to represent the absence of a value, but null
is typically used to represent a deliberate absence of a value, while undefined
is used to represent an unintentional absence of a value.
Points to remember:
- TypeScript variables can be defined using let, const, and var keywords
- let and const variables are block-scoped, while var variables are function-scoped
- Type annotations can be added to variables for type safety
- TypeScript allows optional and default parameter values in functions
Conclusion:
TypeScript provides a strong typing system for variables, which can help prevent runtime errors and make code more predictable. By using let and const keywords, variables can be scoped to specific blocks, making code easier to reason about. Optional and default parameter values in functions can also make code more flexible and easier to use.