Challenge 1: Compiler API

Solve an analysis task with the Compiler API.

Analysis with the Compiler API

In this challenge you will analyze a source file with the Compiler API. Parse the source with ts.createSourceFile, walk the AST with ts.forEachChild, and recognize functions with ts.isFunctionDeclaration. You will extract function parameter counts and names.

Exercise Sum parameter counts

Create a SourceFile from function a(x: number) {} function b(y: string, z: number) {}. Write a visit function that sums the parameter count of each FunctionDeclaration. Walk with ts.forEachChild and print the total.

Show example solution

import ts from "typescript";

const sourceText = "function a(x: number) {} function b(y: string, z: number) {}";
const sf = ts.createSourceFile("app.ts", sourceText, ts.ScriptTarget.Latest, true);

let total = 0;
function visit(node: ts.Node) {
  if (ts.isFunctionDeclaration(node)) {
    total += node.parameters.length;
  }
  ts.forEachChild(node, visit);
}
visit(sf);
console.log(total);

Exercise List function names

Create a SourceFile from function topla() {} function cikar() {}. Write a visit function that prints each FunctionDeclaration's name via node.name.text. Walk with ts.forEachChild.

Show example solution

import ts from "typescript";

const sourceText = "function topla() {} function cikar() {}";
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);
  }
  ts.forEachChild(node, visit);
}
visit(sf);

Test yourself

How do you access the parameter count of a FunctionDeclaration?
- node.arguments.length
- node.parameters.length
- node.params.length
- node.args.length
Show answer

node.parameters.length — FunctionDeclaration.parameters is a ReadonlyArray<ParameterDeclaration>; its count is taken with length. params, args or arguments properties do not exist.

Get the function name

if (ts.isFunctionDeclaration(node) && node.name) {
  console.log(node.name.____);
}

Show answer

if (ts.isFunctionDeclaration(node) && node.name) {
  console.log(node.name.text);
}

Compiler API analysis parts

ts.createSourceFile

Parses the source
ts.forEachChild

Walks the AST
ts.isFunctionDeclaration

Recognizes functions
node.parameters

Accesses parameters

Next lesson: Challenge 2: Transformer

We Are Enhancing Your Experience

Cookie Preferences

Strictly Necessary Cookies

Analytical Cookies