@contrast/require-hook

!Pipeline Status

Intercept calls to require in order to modify or replace exports.

Usage

$3

#### Instantiation

``javascript
const RequireHook = require('./lib');
const requireHook = new RequireHook();
`

The RequireHook constructor accepts a pino
logger as an argument.

#### .resolve(descriptor, ...handlers)

Options:

- descriptor: This can be a string or an object describing the module you want
to intercept. If a string is used, or if the version field of the descriptor
isn't set, all versions of the described module will be matched. Descriptors
can have a name, version, and file property.

- handlers: The remaning arguments are the handlers which will be invoked when
the described module is require'd. Each handler is passed the exported
module and metadata including the module's root directory and its name and
version as seen in its package.json file. If a handler returns a truthy
value, then that value will replace the return value of require.

_Note:_ Registered handlers run _once_ per unique instance of an export
matching a descriptor.

#### .install()

This will monkey-patch Module.prototype.require so that exports can be
intercepted. The monkey-patching will only happen once regardless of how many
times this is invoked.

#### .uninstall()

This will reset Module.prototype.require to its value before being
monkey-patched by the instance.

Examples

Use case: For express versions greater than or equal to 4, intercept the
export of the package's lib/view.js file (relative to the package's base
directory) and apply a tag to the exported function.

`javascript
const RequireHook = require('./lib');
const requireHook = new RequireHook();
requireHook.resolve(
{
name: 'express',
version: '>=4',
file: 'lib/view.js',
},
(xport, metadata) => {
// Read from the package.json:
// - metadata.name
// - metadata.version
// Absolute path to file:
// - metadata.packageDir

// xport === function View() { /.../ }
xport['I was intercepted'] = true;
},
);
`

Use case: Intercept all versions of body-parser and replace the exported
functions.

`javascript
const RequireHook = require('./lib');
const requireHook = new RequireHook();
requireHook.resolve({ name: 'body-parser' }, (xport, metadata) => {
// Read from the package.json:
// - metadata.name
// - metadata.version
// Absolute path to file:
// - metadata.packageDir

// xport === function bodyParser() { /.../ }
return function bodyParserReplacement() {
/.../
};
});
``