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How the TypeScript Compiler Works and Its Components

The TypeScript compiler, also known as tsc, is a command-line tool that compiles TypeScript code into JavaScript code.

The Components Of TypeScript Compiler 🤔

TypeScript is a statically-typed superset of JavaScript that adds optional type annotations, interfaces, and other features to improve the development experience and catch potential errors at compile-time.

Here's an overview of the various components and phases of the TypeScript compiler and compilation process:


The compiler starts by parsing the TypeScript source code(.tsfiles) into an Abstract Syntax Tree (AST). The AST represents the structure and syntax of the source code in a tree-like format. During the parsing phase, the compiler also performs syntax and lexical analysis to identify potential syntax errors.

Type Checking

Next, the TypeScript compiler performs type checking based on the type annotations and inference rules. This step is crucial to catch type-related errors early in the development process. The TypeScript type checker analyzes the type information in the AST and checks if the types are being used correctly according to the language rules. If any type-related errors are detected, the compiler reports them to the developer.


Once the TypeScript code has been parsed and type-checked, the compiler moves to the transformation phase. In this phase, the TypeScript-specific syntax and constructs are transformed into their equivalent JavaScript constructs. For instance, the TypeScript-specific interface construct is removed, and TypeScript type annotations are stripped out, as they have no equivalent in JavaScript.

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After the transformation, the compiler emits the final JavaScript code. This is the output that can be executed by JavaScript engines in browsers or Node.js. The TypeScript compiler can emit different JavaScript versions (ES5, ES6, etc.) based on the specified target in the project's configuration file (usually tsconfig.json).

Source Maps

Optionally, the TypeScript compiler can generate source maps during the emitting phase. Source maps are files that map the generated JavaScript code back to the original TypeScript code. They are useful for debugging purposes, as they allow developers to view and debug their TypeScript code directly in browsers or other debugging tools, even though the actual code being executed is JavaScript.

The TypeScript compiler works by parsing TypeScript code into an AST, performing type checking, transforming TypeScript constructs into JavaScript, and finally emitting the resulting JavaScript code, along with optional source maps.

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