CODEWITHSUNDEEP
javascriptnode.jstypescriptdynamic-import
Terry
Terry

Reputation: 309

Dynamic reloading only part of back-end with dynamic import

In my node backend, I have the following file structure:

project
|-- expensive
|   |-- index.ts
|-- files
|   |-- foo.ts
|   |-- bar.ts
|   `-- baz.ts
|-- tsconfig.json
|-- package.json
`-- index.ts

I want to reload only part of my project (./files/*) without having to restart the entire thing. What I did was use dynamic import:

// inside index.ts...
const client = new Client() as Client;

client.expensive = new Map();
client.files = new Map()

// load each file under the `files` dir
client.loadFiles = async () => {
  const fileNames = readdirSync('./files/')
  fileNames.forEach(async name => {
    const module = await import('./files/' + name); // dynamic import
    client.files.set(module.default.name, module.default)
  })
}

// client.loadExpensive...

// load everything
async function loadAll(reload: boolean = false) {
  await client.loadFiles(reload);
  await client.loadExpensive(reload);
}

loadAll();
startApp();

Then the reload function would be:

// reload all or the specified dir
client.reload = async (dir?: string | undefined) => {
  if (dir) {
    dir = dir.replace(/^\w/, c => c.toUpperCase()); // capitalize
    if (client.hasOwnProperty('load'+dir)) client['load'+dir]();
    else console.error('no such dir')
  } else {
    await loadAll();
  }
}

Problem is while the project loads and reload without error. Adding or removing files under .files/*, then calling .reload() does not seem produce any change. Why is that?

Prior to converting to TS, I used require and cache busting:

// additional reload arg
client.loadFiles = async (reload) => {
  const fileNames = readdirSync('./files/')
  fileNames.forEach(async name => {
    // delete require cache then require the file
    if (reload) delete require.cache[require.resolve(`./${dir}/${name}.ts`)];
    client.files.set(module.default.name, module.default)
  })
}

So i looked at the transpiled js code, it looks like import() use require underneath.

const module = yield Promise.resolve().then(() => __importStar(require('./files/' + name)));

What am I doing wrong? or is this even a good pattern to follow.

Upvotes: 0

Views: 800

Answers (1)

Lauren Yim
Lauren Yim

Reputation: 14128

Because import() compiles to require() (roughly), you'll need to delete the require cache like you did before you used TS.

client.loadFiles = async (reload: boolean) => {
  const fileNames = readdirSync('./files/')
  fileNames.forEach(async name => {
    // Note that if you're using ts-node the extension will be ts not js
    if (reload) delete require.cache[require.resolve(`./files/${name}.js`)]
    const module = await import('./files/' + name); // dynamic import
    client.files.set(module.default.name, module.default)
  })
}

Upvotes: 1

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