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tsc-template

This project provides utilities to facilitate the creation and manipulation of TypeScript Abstract Syntax Trees (ASTs). The key utility is the ast function that works similarly to the @babel/template package but for TypeScript.

Installation

To install the project, run:

npm install tsc-template

Features

AST Generation

Easily create TypeScript ASTs from template strings.

The creation of TypeScript AST is not trivial and has nuances. To simplify that, you can use ast function that consumes a string and returns an AST for it.

import ast from 'tsc-template';
import { isSourceFile } from 'typescript';

const file = ast`const foo = [1, 2, 3]`;
assert(isSourceFile(file));
assertEqual(file.getText(), 'const foo = [1, 2, 3]');

Mix of String and AST Nodes

Use TypeScript nodes directly in the code as if they are simple strings.

When you work with massive TS generation, sometimes you need to use nodes created in one place, in another. With the plain TypeScript, you would need to create a TS transformer or create all the tree manually. However, with power of template literals, you can use the nodes directly in the code you provide to ast function.

import ast from 'tsc-template';
import { factory } from 'typescript';

const fooId = factory.createIdentifier('foo');
const file = ast`const ${fooId} = [1, 2, 3]`;

assertEqual(file.getText(), 'const foo = [1, 2, 3]');

Smart Result Injection

Inject the result of one ast function to another; no complex selectors required.

What if you have created a good chunk of the code using the ast function and want to inject it into another chunk? No problem: just use the result of one ast function as a part of another! The smart injection system will find the correct node, so you don't need to create complex selectors.

import ast from 'tsc-template';

const file = ast`const foo = ${ast`[1, 2, 3]`}`;

assertEqual(file.getText(), 'const foo = [1, 2, 3];');

Tags for Custom AST Extractions

Use extractor tags to select only a part of the code you need.

Sometimes, the code you can create via ast function is represented incorrectly in TypeScript AST. E.g., when you declare a function in the module root, it will be FunctionDeclaration while the function assigned to the variable is FunctionExpression. What to do?

It's simple. Use extractor tags! %{ and }% would allow you to select the correct part of the code you want to have as AST.

import ast from 'tsc-template';

const functionExpression = ast`const b = %{ function b() {} }%`;
const file = ast`const x = ${functionExpression}`;
assertEquals(file.getText(), 'const x = function b() {};');

License

This project is licensed under the Apache-2.0 License.