Summary - Compiler API

Write a simple code analysis tool with the Compiler API.

Compiler API summary

Three pieces together give you full code analysis with the Compiler API: ts.createProgram sets up the compilation, program.getTypeChecker() provides symbol and type resolution, and ts.forEachChild walks the AST nodes. For in-memory sources you supply a CompilerHost; nothing is written to disk.

const program = ts.createProgram(files, opts, host);
const checker = program.getTypeChecker();

function visit(node: ts.Node) {
  // resolve types with checker; descend with forEachChild
  ts.forEachChild(node, visit);
}
visit(sourceFile);

Exercise List functions

Create a source file with two functions: function topla(a: number, b: number): number { return a + b; } and function yaz(metin: string) { console.log(metin); }. Use ts.createSourceFile to build the SourceFile. Write a visit function; find each function with ts.isFunctionDeclaration and print name: parameterCount. Walk the tree with ts.forEachChild.

Show example solution

import ts from "typescript";

const sourceText = "function topla(a: number, b: number): number { return a + b; }\nfunction yaz(metin: string) { console.log(metin); }";
const sf = ts.createSourceFile("app.ts", sourceText, ts.ScriptTarget.Latest, true);

function visit(node: ts.Node) {
  if (ts.isFunctionDeclaration(node) && node.name) {
    console.log(`${node.name.text}: ${node.parameters.length}`);
  }
  ts.forEachChild(node, visit);
}
visit(sf);

Test yourself

Which trio comes together for full code analysis?
- getTypeChecker + writeFile + readFile
- getSourceFile + getText + console.log
- createProgram + TypeChecker + forEachChild
- createSourceFile + JSON.stringify + writeFile
Show answer

createProgram + TypeChecker + forEachChild — createProgram sets up the compilation, the TypeChecker resolves meaning and forEachChild walks the syntax tree; together they give full analysis.

TypeChecker call

const program = ts.createProgram([fileName], { noLib: true }, host);
const checker = program.____;

Show answer

const program = ts.createProgram([fileName], { noLib: true }, host);
const checker = program.getTypeChecker();

Compiler API summary

createProgram

Compilation object
getSourceFiles

Source files
getTypeChecker

Semantic resolver
forEachChild

AST traversal

Next lesson: What is a transformer?

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