lazy-cache

What is lazy-cache?

The lazy-cache npm package is designed to lazily require modules, meaning that the modules are only required when they are actually needed. This can help improve the performance of your application by deferring the loading of modules until they are used.

What are lazy-cache's main functionalities?

Lazy Loading of Modules

This feature allows you to defer the loading of a module until it is actually used in your code. In the example, the 'fs' module is not loaded until the 'readFileSync' method is called.

const lazy = require('lazy-cache')(require);
const fs = lazy('fs');

// fs is not loaded until it is used
fs.readFileSync('path/to/file.txt', 'utf8');

Custom Lazy Loading

You can also use lazy-cache to lazily load your own custom modules. In this example, the './customModule' is not loaded until 'someFunction' is called.

const lazy = require('lazy-cache')(require);
const customModule = lazy('./customModule');

// customModule is not loaded until it is used
customModule.someFunction();

Other packages similar to lazy-cache

require-lazy

The require-lazy package provides similar functionality by allowing you to lazily require modules. It offers a simple API for deferring the loading of modules until they are needed, similar to lazy-cache.

proxyquire

Proxyquire is a powerful tool for mocking dependencies during testing, but it also supports lazy loading of modules. It allows you to mock out dependencies and control when they are loaded, providing more flexibility compared to lazy-cache.

import-lazy

Import-lazy is another package that allows you to lazily import modules. It uses ES6 proxies to defer the loading of modules until they are accessed, offering a modern alternative to lazy-cache.

README

lazy-cache

Cache requires to be lazy-loaded when needed.

Install

Install with npm:

$ npm install --save lazy-cache

Heads up!

It's suprising how many libraries are in the average dependency tree that don't belong there for one reason or another. Either because they were accidentally listed as dependencies instead of devDepedencies, or they are required in a file as variables, but the variable is never actually used (poor linting), and so on. Or because the maintainer made the decision to add the deps, even though they will never (or can't ever) be used by 99.9% of users.

Worse, many libraries like chalk and shelljs actually execute code when require() is called!? (shelljs was modifying the String.prototype, and chalk loops over some objects to dynamically create methods). In other words, they do something like this:

// in the main export of a library, if you do this it will
// automatically modify the String.prototype _globally_, 
// the moment node.js loads the dependency tree
String.prototype.foo = function() {};

// same if you do something like this
// (dont' do this, ever. wrap this kind of code in a function
// and allow implementors to decide when to call it)
while (foo) {
  // do stuff
}

In any case, just having these libraries in your dependency tree somewhere means that their code will excecute the moment you run your application even if the libraries are never called by your application or any other code anywhere in the tree.

solution

lazy-cache doesn't use any "magic", it uses native, plain-vanilla, tried and true javascript getters to call node's require() system.

Faster, safer code

There main advantage to this, the main is that requires are loaded on demand, so only code that is actually used will ever be loaded. As a result, applications will load faster (sometimes much faster - we've seen load times drop from ~1 second to less than 50 milliseconds).

Moreover, in some cases this also avoids inadvertently loading libraries that execute code or modifies globals, etc.

webpack users

If you use webpack and are experiencing issues with lazy-cache, this is a known bug caused by webpack, not lazy-cache. There is a solution though, you can use unlazy-loader, a webpack loader that fixes the webpack bug.

Usage

var utils = require('lazy-cache')(require);

Use as a property on lazy

The module is also added as a property to the lazy function so it can be called without having to call a function first.

var utils = require('lazy-cache')(require);

// `npm install glob`
utils('glob');

// glob sync
console.log(utils.glob.sync('*.js'));

// glob async
utils.glob('*.js', function (err, files) {
  console.log(files);
});

Use as a function

var utils = require('lazy-cache')(require);
var glob = utils('glob');

// `glob` is a now a function that may be called when needed
glob().sync('foo/*.js');

Aliases

An alias may be passed as the second argument if you don't want to use the automatically camel-cased variable name.

Example

var utils = require('lazy-cache')(require);

// alias `ansi-yellow` as `yellow`
utils('ansi-yellow', 'yellow');
console.log(utils.yellow('foo'));

Dot notation may also be used in the alias to create an object hierarchy.

Example

var utils = require('lazy-cache')(require);
utils('ansi-cyan', 'color.cyan');
utils('ansi-yellow', 'color.yellow');
utils('ansi-magenta', 'color.magenta');
console.log(utils.color.cyan('foo'));
console.log(utils.color.yellow('bar'));
console.log(utils.color.magenta('baz'));

Browserify usage

Example

var utils = require('lazy-cache')(require);
// temporarily re-assign `require` to trick browserify
var fn = require;
require = utils;
// list module dependencies (here, `require` is actually `lazy-cache`)
require('glob');
require = fn; // restore the native `require` function

/**
 * Now you can use glob with the `utils.glob` variable
 */

// sync
console.log(utils.glob.sync('*.js'));

// async
utils.glob('*.js', function (err, files) {
  console.log(files.join('\n'));
});

Kill switch

To force lazy-cache to immediately invoke all dependencies, do:

process.env.UNLAZY = true;

About

Related projects

lint-deps: CLI tool that tells you when dependencies are missing from package.json and offers you a… more | homepage

Contributing

Pull requests and stars are always welcome. For bugs and feature requests, please create an issue.

Contributors

Commits	Contributor
31	jonschlinkert
27	doowb

Building docs

(This document was generated by verb-generate-readme (a verb generator), please don't edit the readme directly. Any changes to the readme must be made in .verb.md.)

To generate the readme and API documentation with verb:

$ npm install -g verb verb-generate-readme && verb

Running tests

Install dev dependencies:

$ npm install -d && npm test

Author

Jon Schlinkert

• github/jonschlinkert
• twitter/jonschlinkert

License

Copyright © 2016, Jon Schlinkert. Released under the MIT license.

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This file was generated by verb-generate-readme, v0.2.0, on November 07, 2016.