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TypeScript

Reading

Learning Outcomes

  • Types in programming
  • Pros & Cons of strict types
  • TypeScript concepts & basic syntax
  • Using TypeScript in a JavaScript application

Types in Programming

Computer programming languages can be distinguished between strongly typed and loosely typed.

Strongly Typed

  • Variables must be defined with specific data types.
  • Language makes a distinction between numeric data types (e.g. int, float, double precision).
  • Arrays can only contain items of the same data type
  • Program code is checked at compile time for mismatch between variable definition and subsequent updates. Mismatches generate an error and prevent program compilation.
  • Examples include Java, C#, C++, & Swift.

Loosely Typed

  • Variables can be defined without a specific data type.
  • Language doesn't distinguish between different numeric data types
  • Arrays can contain items of different data types
  • Compiler implies datatype based on initial value and may allow assigning new values of a different data type.
  • Examples include JavaScript & Python

Pros & Cons of Strict Types

Pros

  • Catches potential data errors at compile time before a program reaches real users
  • Enforces code consistency
  • Removes ambiguity about objects imported into other applications
  • Enables static type checking and hints in IDE

Cons

  • Adds significant program structure & execution overhead to JavaScript projects.
  • JavaScript programs that use TypeScript cannot be run in a web browser without explicit compilation
  • Can add significant overhead to JavaScript object definition

TypeScript Concepts

TypeScript is a Microsoft project that implements strict types in JavaScript projects through an external layer (compiler), rather than through direct support in the JavaScript language.

Projects using TypeScript must define types (objects) in files with a special .ts or .tsx extension and compile them to JavaScript with a build system such as https://webpack.js.org/

  • TypeScript code compiles to native JavaScript.
  • TypeScript includes rules about how different kinds of values can be used (e.g. in math operations)