🧀 Magicast
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Programmatically modify JavaScript and TypeScript source codes with a simplified, elegant and familiar syntax. Built on top of the AST parsed by recast and babel.
❯ 🧙🏼 Magical modify a JS/TS file and write back magically just like JSON!
❯ 🔀 Exports/Import manipulate module's imports and exports at ease
❯ 💼 Function Arguments easily manipulate arguments passed to a function call, like defineConfig()
❯ 🎨 Smart Formatting preseves the formatting style (quotes, tabs, etc.) from the original code
❯ 🧑💻 Readable get rid of the complexity of AST manipulation and make your code super readable
Install
Install npm package:
yarn add --dev magicast
npm install -D magicast
pnpm add -D magicast
Import utilities:
import { parseModule, generateCode, builders, createNode } from "magicast";
const { parseModule, generateCode, builders, createNode } = require("magicast");
Examples
Example: Modify a file:
config.js
:
export default {
foo: ["a"],
};
Code to modify and append b
to foo
prop of defaultExport:
import { loadFile, writeFile } from "magicast";
const mod = await loadFile("config.js");
mod.exports.default.foo.push("b");
await writeFile(mod, "config.js");
Updated config.js
:
export default {
foo: ["a", "b"],
};
Example: Directly use AST utils:
import { parseModule, generateCode } from "magicast";
const mod = parseModule(`export default { }`);
mod.exports.default.foo ||= [];
mod.exports.default.foo.push("b");
mod.exports.default.foo.unshift("a");
const { code, map } = generateCode(mod);
Generated code:
export default {
foo: ["a", "b"],
};
Example: Get the AST directly:
import { parseModule, generateCode } from "magicast";
const mod = parseModule(`export default { }`);
const ast = mod.exports.default.$ast
Example: Function arguments:
import { parseModule, generateCode } from "magicast";
const mod = parseModule(`export default defineConfig({ foo: 'bar' })`);
const options = mod.exports.default.$type === 'function-call'
? mod.exports.default.$args[0]
: mod.exports.default;
console.log(options.foo)
Example: Create a function call:
import { parseModule, generateCode, builders } from "magicast";
const mod = parseModule(`export default {}`);
const options = mod.exports.default.list = builders.functionCall('create', [1, 2, 3])
console.log(mod.generateCode())
Notes
As JavaScript is a very dynamic language, you should be aware that Magicast's convention CAN NOT cover all possible cases. Magicast serves as a simple and maintainable interface to update static-ish JavaScript code. When interacting with Magicast node, be aware that every option might have chance to throw an error depending on the input code. We recommend to always wrap the code in a try/catch
block (even better to do some defensive coding), for example:
import { loadFile, writeFile } from "magicast";
function updateConfig() {
try {
const mod = await loadFile("config.js");
mod.exports.default.foo.push("b");
await writeFile(mod);
} catch (e) {
console.error('Unable to update config.js')
console.error('Please update it manually with the following instructions: ...')
}
}
High Level Helpers
We also experiment to provide a few high level helpers to make common tasks easier. You could import them from magicast/helpers
. They might be moved to a separate package in the future.
import {
deepMergeObject,
addNuxtModule,
addVitePlugin,
} from "magicast/helpers";
We recommend to check out the source code and test cases for more details.
Development
- Clone this repository
- Install latest LTS version of Node.js
- Enable Corepack using
corepack enable
- Install dependencies using
pnpm install
- Run interactive tests using
pnpm dev
License
Made with 💛
Published under MIT License.