Fakesync

fakesync makes it easy to turn any function into a fake async call for front-end testing. You can add delays, simulate failures, and make fake data behave like it’s coming from a real back-end. It’s small, simple, and doesn’t require a full mock server—perfect when you just need realistic responses without extra setup.

Installation

Install from npm:

npm install fakesync

Or require locally if testing:

const fakesync = require('./index');

API

fakesync.registerDefaults(options)

Set global default options.

• options.minDelay: Minimum delay in ms (default 0)
• options.maxDelay: Maximum delay in ms (default 500)
• options.failRate: Probability of rejection (0-1, default 0)

fakesync.register(funcs, options)

Register functions to be wrapped.

• funcs: Object with function names as keys and functions as values
• options: Override options for these functions

After registering, fakesync.register({...}) returns an object whose methods are Promise-returning wrappers around the original functions. Call the returned methods (not properties added to the fakesync object) to get the delayed/possibly failing behavior.

Example

See example.js for a complete example.

const fakesync = require('fakesync');

fakesync.registerDefaults({ minDelay: 100, maxDelay: 1000, failRate: 0.1 });

function mySyncFunc(x) {
  return x * 2;
}

const api = fakesync.register({ mySyncFunc });

(async () => {
  try {
    const result = await api.mySyncFunc(5); // 10, after random delay
    console.log(result);
  } catch (err) {
    console.error('Function failed:', err);
  }
})();

please feel free to contribute 🙏

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TypeScript

This package provides a declaration file so TypeScript-aware editors and tooling can understand dynamically registered functions. After installing, you can import normally and call your registered handlers with type help:

import fakesync from 'fakesync';

fakesync.register({ handleSignInClick: () => {/* ... */} });

// TypeScript will understand fakesync.handleSignInClick exists at runtime
// but may still be `any`-typed unless you declare a stronger signature.