Identifying arrow functions using the Typescript Compiler API: A guide

Question

Identifying arrow functions using the Typescript Compiler API: A guide

I've been trying to mimic the example provided in the TypeScript wiki on Using the Type Checker but I'm having trouble detecting arrow functions.

For instance:

/**
 * Hello
 */
export const hello = (): string => 'hello';

My visitor doesn't recognize this as an arrow function:

function visit(node: ts.Node) {
   console.log(node.kind, ts.isArrowFunction(node)); // -> 236, false

However, standard functions are being correctly identified:

For example:

/**
 * Hello
 */
export function hello (): string {return 'hello'};

This is recognized by the visitor using isFunctionDeclaration

function visit(node: ts.Node) {
   console.log(node.kind, ts.isFunctionDeclaration(node)); // -> 255, true

What am I missing here? How can I successfully detect arrow functions?

typescript typescript-compiler-api

Answer 1

Answer №1

Check out this code snippet on ts-ast-viewer.com:

https://i.sstatic.net/SDHbJ.png

Upon inspection, you'll notice a nested structure starting from a VariableStatement all the way to an ArrowFunction initializer within a VariableDeclaration.

You can also traverse recursively downwards as shown below:

function findDescendantArrowFunction(node: ts.Node) {
  if (ts.isArrowFunction(node)) {
    return node;
  } else {
    return ts.forEachChild(node, findDescendantArrowFunction);
  }
}

const arrowFunc = findDescendantArrowFunction(sourceFile);

Answer 2

Check out this code snippet on ts-ast-viewer.com:

https://i.sstatic.net/SDHbJ.png

Upon inspection, you'll notice a nested structure starting from a VariableStatement all the way to an ArrowFunction initializer within a VariableDeclaration.

You can also traverse recursively downwards as shown below:

function findDescendantArrowFunction(node: ts.Node) {
  if (ts.isArrowFunction(node)) {
    return node;
  } else {
    return ts.forEachChild(node, findDescendantArrowFunction);
  }
}

const arrowFunc = findDescendantArrowFunction(sourceFile);

Identifying arrow functions using the Typescript Compiler API: A guide

Answer №1

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