javascript / expert
Snippet
Custom ESM Loaders for Runtime Module Instrumentation
Node.js allows customizing the ES module resolution and loading process via loader hooks. This enables on-the-fly transformations (like TypeScript compilation) or security sandboxing by intercepting every 'import' statement in the application.
snippet.js
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// loader.mjsexport async function load(url, context, nextLoad) {const result = await nextLoad(url, context);if (url.endsWith('.ts')) {return {format: 'module',shortCircuit: true,source: transformCode(result.source)};}return result;}
nodejs
Breakdown
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export async function load(url, context, nextLoad)
The hook called by Node.js whenever a module needs to be loaded into the source.
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const result = await nextLoad(url, context);
Calls the default loader or the next hook in the chain to get the raw source.
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shortCircuit: true,
Informs Node.js that this hook has handled the request and no further hooks are needed.
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source: transformCode(result.source)
Applies custom logic to the source code before it is parsed by V8.