TypeScript · Beginner
Simple Interfaces
Interfaces are used to describe the shape of an object. They act as a contract for what properties an object should have.
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Beginner TypeScript exercises
Read these Beginner TypeScript snippets line by line — each one comes with a written breakdown of what the code does and why.
TypeScript · Beginner
Type Annotations
Type annotations allow us to explicitly specify the type of a variable. This helps the compiler catch errors if we try to assign a value of the wrong type.
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Basic Function Types
In TypeScript, you can define the types of the parameters a function receives and the type of the value it returns.
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Defining Arrays
TypeScript allows you to define arrays that contain only a specific type of element, preventing accidental mixed-type arrays.
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Union Types
Union types allow a variable to be one of several types. This is useful when a value could legitimately be different types.
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Optional Chaining
The optional chaining operator (?.) permits reading the value of a property deep within a chain of objects without having to check if each reference is valid.
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Nullish Coalescing
The nullish coalescing operator (??) returns its right-hand operand when its left-hand operand is null or undefined. Unlike ||, it treats 0 as a valid value.
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Type Assertions
Type assertions are a way to tell the compiler to treat a value as a specific type when you have more information about it than TypeScript does.
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Numeric Enums
Enums allow a developer to define a set of named constants, making it easier to document intent or create a set of distinct cases.
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Readonly Modifier
The 'readonly' keyword makes a property immutable. It can only be assigned a value at declaration or within the constructor of the class.
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Basic Type Annotations
Type annotations allow you to explicitly state what type of data a variable should hold, helping catch errors during development.
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Defining an Interface
An Interface defines the structure of an object, ensuring it has specific properties with specific types.
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Function Parameter Types
In TypeScript, you can specify types for both function parameters and the value the function returns.
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Array Type Syntax
You can define an array that only allows a specific type of element by adding square brackets after the type name.
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Tuple Types
A tuple is a specialized array where you know exactly how many elements it contains and which types are at specific positions.
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Readonly Properties
The 'readonly' modifier makes a property immutable after the object is first initialized, preventing accidental changes to sensitive data.
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The 'unknown' Type
The 'unknown' type is a safer version of 'any'. You cannot perform operations on an 'unknown' value until you verify its type using a type check.
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Type Aliases for Objects
Type aliases allow you to give a custom name to an object structure, making it easy to reuse the same shape across your code without using interfaces.
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Optional Chaining
Optional chaining allows you to safely access properties that may be null or undefined. If any part of the chain is missing, it returns undefined instead of throwing a runtime error.
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Nullish Coalescing Operator
The nullish coalescing operator (??) returns the right-hand value only if the left-hand value is null or undefined. Unlike the OR (||) operator, it doesn't trigger for empty strings or 0.
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The 'void' Return Type
In TypeScript, 'void' is used to indicate that a function does not return any value. It helps prevent logic errors where a return value might be expected but doesn't exist.
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String Enums
String enums allow you to define a set of named constants with string values. They provide better readability and easier debugging compared to numeric enums because the values are descriptive.
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The 'never' Type
The 'never' type represents values that never occur. It is used for functions that always throw an error or contain infinite loops, meaning they never reach a return statement.
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Literal Types
Literal types allow you to specify the exact value a string, number, or boolean must have, rather than just any value of that type.
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Type Guards with typeof
Type guards use runtime checks to narrow down a union type to a specific type within a block of code.
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Basic Class with Access Modifiers
Access modifiers like 'public' and 'private' control whether class members can be accessed from outside the class.
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Function Overloads
Function overloads allow you to define multiple ways a function can be called, providing better type checking for different input combinations.
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Array Type Annotations
You can specify the type of elements allowed in an array using the square bracket syntax (type[]) after the type name.
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Typed Function Parameters
TypeScript allows you to define explicit types for function arguments and the expected return type to prevent logic errors.
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Optional Function Parameters
Function parameters can be marked as optional using the question mark syntax, allowing them to be omitted during calls.
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