I have created a number of String.prototype functions which for maintainability I'd like to have in its own file. That is, I'd like to include the file in a javascript project and thus have all the String functions defined.
I could create a module that exports each function, but then I'd have to assign each function as its own String prototype, yes? Something like
var myStringFunctions = require("myStringFunctions");
String.prototype.func1 = myStringFunctions.func1;
Is there a way to include such a file so that the prototypes are defined as part of the inclusion?
Try it, you will see your code and using require("./myStringFunctions"); works just fine.
./myStringFunctions.js
String.prototype.func1 = function() {
return this.toUpperCase(this);
};
./index.js
require("./myStringFunctions");
console.log("foo".func1()); // FOO
If your JS is going to run in the browser, you can use JS modules with the import and export syntax if you use a module bundling build tool like Webpack: https://webpack.js.org/ .
If your JS is running in a Node.js environment, modules are supported: https://www.w3schools.com/nodejs/nodejs_modules.asp
I'm finding some problems when loading certain .js module via require.js
Problem is: I only need to load certain module in some pages, not the entire website. Therefore I'm placing code this way:
if($('.module-news').length > 0 + $('.module-ticket-euromillones-multiple').length + $('.module-news-page').length > 0) {
require('_modules/news-grid').init();
}
This code search in the HTML if a class="module-news" exists (news page). If so, then load the module with the javascript.
That is NOT working. The IF is evaluating correctly, but module news-grid is ALWAYS loading no matter .module-news exists or not.
I found out that if I change the string of the module path for a variable, then requires behaves correctly, but that makes no sense. This how, following code works:
var name = "_modules/news-grid";
if($('.module-news').length > 0 + $('.module-ticket-euromillones-multiple').length + $('.module-news-page').length > 0) {
require(name).init();
}
Is this a known issue with require? Am I missing something? (maybe in the requirejs.config settings?
Help appreciated
Solution
You should be using the regular RequireJS idiom for calling require:
if (...) {
require(['_modules/news-grid'], function (news_grid) {
news_grid.init();
});
}
Why It Fails
You are using RequireJS' feature which lets you write require calls in the CommonJS format var module = require("module name"). You cannot use it for loading modules conditionally.
The call require('module name') (with a string as the first argument rather than a dependency array) is a convenience. It will return a module but if and only if the module is already loaded. If the module is not already loaded, then the call will fail. The only reason you don't have to worry about pre-loading the modules before calling require('module name') is that RequireJS does it for you.
define(function (require) {
var foo = require('foo');
});
is interpreted by RequireJS as:
define(['require', 'foo'], function (require) {
var foo = require('foo');
});
It scans the function for calls to require in the CommonJS idiom and generates a list of modules that it loads before executing the module. Conditionals are completely transparent to this process. Any require call with a string as the first parameter will be detected and the module it means to load will be added to the dependencies loaded before define's callback is called...
RequireJS won't detect those cases where something else than a string is passed to require. If you write:
var name = "foo";
var foo = require(name);
RequireJS will not know that you want to load foo and will not add foo to the list of dependencies. Is this a solution? No, because remember what I said earlier require('module name') will return a module, and not fail, only if the module is already loaded.
If you want your module to be loaded conditionally, then abandon the CommonJS idiom.
This is b.js
var something = "hooorraaaaay!!!";
And this is a.js
require( './b.js' );
console.log(something);
Why isn't something being recognised within a.js. I understand that it has been declared with var, but my understanding is that any variable declared outside a function should act global. So why isn't this working?
Node modules are each in their own scope. By default, nothing in module a is visible to module b. Doing a require() on a module is NOT like including the source. It loads the file runs the code and then the only things that are available to the outside world are:
Any functions or properties that are explicitly exported from the module by assigning to module.exports.
Any functions or properties that are explicitly assigned to the global object in node.
So, if you want something in b.js to be exposed to the outside world, you do like this:
// b.js
module.exports.callMe = function() {
console.log("I'm in module b");
}
And, then in a.js, you can do this:
// a.js
var b = require('./b.js');
b.callMe();
This is how the module system works in node.js. It is very different than just including a <script> tag in a browser web page. You can read more about the module system in these references:
Understanding module.exports and exports in Node.js
What is the purpose of Node.js module.exports and how do you use it?
Node.js Handbook - How require() Actually Works
Internally, node.js loads a module's code and then inserts it into a wrapper function. So, each top level variable in a node module is actually only a local variable in that module function. This is why nothing is globally declared or shared by default. It is done this way on purpose so that each module comes with it's own private area for storing it's state and will not, by default, interfere with the variables of any other module.
You then explicitly export only the property/function interfaces that you want to make public and even then, they are still not exported as public symbols so again they cannot conflict with anything else.
So, the b.js code above actually gets transformed into this when node.js runs it:
(function (exports, module, require, __filename, __dirname){
module.exports.callMe = function() {
console.log("I'm in module b");
}
})(...);
The (...) contains actual variables that are passed to the module.
Let me assume you are using node.js judging from the require function.
node.js wraps each file in its own scope. this has nothing to do with the use of var keyword. every file in node.js is called a module.
Now let's say you want to include a module, here comes require, you have used it right.
But since your module doesn't export anything, it's useless when it's included in some other module.
So at the end of your b.js file, add the following line :
module.exports.something = something;
Now we can finally use our exported variable :
var b = require('./b.js');
console.log('Something is : ' + b.something);
I am starting to use RequireJS now and I was already able to add my project dependencies but I still cannot add a jQuery anonymous function yet.
For example, with my normal_file.js I do something like:
normal_file.js:
define(['dependency1'], function(Dependency) {
var Test1 = ...;
return Test1;
});
Bu from a file that has no module, like the example below, I don't know how to encapsulate it:
lib_file.js:
(function ($) {
// Do stuff...
})(window.jQuery);
the lib_file was not made by me and I'm not sure on how it really works, but I would gess it is an anonymous auto-executed function, is that so?.
Anyway, my goal is to use both files in my main code, like below:
main.js:
requirejs.config({
baseUrl:'/static/editorial/js/',
paths: {
jquery: 'third_party/jquery-1.10.2',
react: 'third_party/react-with-addons'
}
});
var dependencies = [
'third_party/react-with-addons',
'third_party/jquery-1.10.2',
'build/utils/normal_file,
'third_party/lib_file
];
require(dependencies, function(React, $, Test1, ??) {
// do my stuff
});
How should I encapsulate that anonymous function in order to add it as a dependency to my main file?
From the RequireJS docs:
Ideally the scripts you load will be modules that are defined by
calling define(). However, you may need to use some traditional/legacy
"browser globals" scripts that do not express their dependencies via
define(). For those, you can use the shim config. To properly express
their dependencies.
Read this: http://requirejs.org/docs/api.html#config-shim
It has a really good explanation of what you have to do, and gives a nice example.
Basically, you just need to set up a shim config for lib_file.js so Require knows to load the right dependencies before giving you access to that script.
What is the purpose of Node.js module.exports and how do you use it?
I can't seem to find any information on this, but it appears to be a rather important part of Node.js as I often see it in source code.
According to the Node.js documentation:
module
A reference to the current
module. In particular module.exports
is the same as the exports object. See
src/node.js for more information.
But this doesn't really help.
What exactly does module.exports do, and what would a simple example be?
module.exports is the object that's actually returned as the result of a require call.
The exports variable is initially set to that same object (i.e. it's a shorthand "alias"), so in the module code you would usually write something like this:
let myFunc1 = function() { ... };
let myFunc2 = function() { ... };
exports.myFunc1 = myFunc1;
exports.myFunc2 = myFunc2;
to export (or "expose") the internally scoped functions myFunc1 and myFunc2.
And in the calling code you would use:
const m = require('./mymodule');
m.myFunc1();
where the last line shows how the result of require is (usually) just a plain object whose properties may be accessed.
NB: if you overwrite exports then it will no longer refer to module.exports. So if you wish to assign a new object (or a function reference) to exports then you should also assign that new object to module.exports
It's worth noting that the name added to the exports object does not have to be the same as the module's internally scoped name for the value that you're adding, so you could have:
let myVeryLongInternalName = function() { ... };
exports.shortName = myVeryLongInternalName;
// add other objects, functions, as required
followed by:
const m = require('./mymodule');
m.shortName(); // invokes module.myVeryLongInternalName
This has already been answered but I wanted to add some clarification...
You can use both exports and module.exports to import code into your application like this:
var mycode = require('./path/to/mycode');
The basic use case you'll see (e.g. in ExpressJS example code) is that you set properties on the exports object in a .js file that you then import using require()
So in a simple counting example, you could have:
(counter.js):
var count = 1;
exports.increment = function() {
count++;
};
exports.getCount = function() {
return count;
};
... then in your application (web.js, or really any other .js file):
var counting = require('./counter.js');
console.log(counting.getCount()); // 1
counting.increment();
console.log(counting.getCount()); // 2
In simple terms, you can think of required files as functions that return a single object, and you can add properties (strings, numbers, arrays, functions, anything) to the object that's returned by setting them on exports.
Sometimes you'll want the object returned from a require() call to be a function you can call, rather than just an object with properties. In that case you need to also set module.exports, like this:
(sayhello.js):
module.exports = exports = function() {
console.log("Hello World!");
};
(app.js):
var sayHello = require('./sayhello.js');
sayHello(); // "Hello World!"
The difference between exports and module.exports is explained better in this answer here.
Note that the NodeJS module mechanism is based on CommonJS modules which are supported in many other implementations like RequireJS, but also SproutCore, CouchDB, Wakanda, OrientDB, ArangoDB, RingoJS, TeaJS, SilkJS, curl.js, or even Adobe Photoshop (via PSLib).
You can find the full list of known implementations here.
Unless your module use node specific features or module, I highly encourage you then using exports instead of module.exports which is not part of the CommonJS standard, and then mostly not supported by other implementations.
Another NodeJS specific feature is when you assign a reference to a new object to exports instead of just adding properties and methods to it like in the last example provided by Jed Watson in this thread. I would personally discourage this practice as this breaks the circular reference support of the CommonJS modules mechanism. It is then not supported by all implementations and Jed example should then be written this way (or a similar one) to provide a more universal module:
(sayhello.js):
exports.run = function() {
console.log("Hello World!");
}
(app.js):
var sayHello = require('./sayhello');
sayHello.run(); // "Hello World!"
Or using ES6 features
(sayhello.js):
Object.assign(exports, {
// Put all your public API here
sayhello() {
console.log("Hello World!");
}
});
(app.js):
const { sayHello } = require('./sayhello');
sayHello(); // "Hello World!"
PS: It looks like Appcelerator also implements CommonJS modules, but without the circular reference support (see: Appcelerator and CommonJS modules (caching and circular references))
Some few things you must take care if you assign a reference to a new object to exports and /or modules.exports:
1. All properties/methods previously attached to the original exports or module.exports are of course lost because the exported object will now reference another new one
This one is obvious, but if you add an exported method at the beginning of an existing module, be sure the native exported object is not referencing another object at the end
exports.method1 = function () {}; // exposed to the original exported object
exports.method2 = function () {}; // exposed to the original exported object
module.exports.method3 = function () {}; // exposed with method1 & method2
var otherAPI = {
// some properties and/or methods
}
exports = otherAPI; // replace the original API (works also with module.exports)
2. In case one of exports or module.exports reference a new value, they don't reference to the same object any more
exports = function AConstructor() {}; // override the original exported object
exports.method2 = function () {}; // exposed to the new exported object
// method added to the original exports object which not exposed any more
module.exports.method3 = function () {};
3. Tricky consequence. If you change the reference to both exports and module.exports, hard to say which API is exposed (it looks like module.exports wins)
// override the original exported object
module.exports = function AConstructor() {};
// try to override the original exported object
// but module.exports will be exposed instead
exports = function AnotherConstructor() {};
the module.exports property or the exports object allows a module to select what should be shared with the application
I have a video on module_export available here
When dividing your program code over multiple files, module.exports is used to publish variables and functions to the consumer of a module. The require() call in your source file is replaced with corresponding module.exports loaded from the module.
Remember when writing modules
Module loads are cached, only initial call evaluates JavaScript.
It's possible to use local variables and functions inside a module, not everything needs to be exported.
The module.exports object is also available as exports shorthand. But when returning a sole function, always use module.exports.
According to: "Modules Part 2 - Writing modules".
the refer link is like this:
exports = module.exports = function(){
//....
}
the properties of exports or module.exports ,such as functions or variables , will be exposed outside
there is something you must pay more attention : don't override exports .
why ?
because exports just the reference of module.exports , you can add the properties onto the exports ,but if you override the exports , the reference link will be broken .
good example :
exports.name = 'william';
exports.getName = function(){
console.log(this.name);
}
bad example :
exports = 'william';
exports = function(){
//...
}
If you just want to exposed only one function or variable , like this:
// test.js
var name = 'william';
module.exports = function(){
console.log(name);
}
// index.js
var test = require('./test');
test();
this module only exposed one function and the property of name is private for the outside .
There are some default or existing modules in node.js when you download and install node.js like http, sys etc.
Since they are already in node.js, when we want to use these modules we basically do like import modules, but why? because they are already present in the node.js. Importing is like taking them from node.js and putting them into your program. And then using them.
Whereas Exports is exactly the opposite, you are creating the module you want, let's say the module addition.js and putting that module into the node.js, you do it by exporting it.
Before I write anything here, remember, module.exports.additionTwo is same as exports.additionTwo
Huh, so that's the reason, we do like
exports.additionTwo = function(x)
{return x+2;};
Be careful with the path
Lets say you have created an addition.js module,
exports.additionTwo = function(x){
return x + 2;
};
When you run this on your NODE.JS command prompt:
node
var run = require('addition.js');
This will error out saying
Error: Cannot find module addition.js
This is because the node.js process is unable the addition.js since we didn't mention the path. So, we have can set the path by using NODE_PATH
set NODE_PATH = path/to/your/additon.js
Now, this should run successfully without any errors!!
One more thing, you can also run the addition.js file by not setting the NODE_PATH, back to your nodejs command prompt:
node
var run = require('./addition.js');
Since we are providing the path here by saying it's in the current directory ./ this should also run successfully.
A module encapsulates related code into a single unit of code. When creating a module, this can be interpreted as moving all related functions into a file.
Suppose there is a file Hello.js which include two functions
sayHelloInEnglish = function() {
return "Hello";
};
sayHelloInSpanish = function() {
return "Hola";
};
We write a function only when utility of the code is more than one call.
Suppose we want to increase utility of the function to a different file say World.js,in this case exporting a file comes into picture which can be obtained by module.exports.
You can just export both the function by the code given below
var anyVariable={
sayHelloInEnglish = function() {
return "Hello";
};
sayHelloInSpanish = function() {
return "Hola";
};
}
module.export=anyVariable;
Now you just need to require the file name into World.js inorder to use those functions
var world= require("./hello.js");
The intent is:
Modular programming is a software design technique that emphasizes
separating the functionality of a program into independent,
interchangeable modules, such that each contains everything necessary
to execute only one aspect of the desired functionality.
Wikipedia
I imagine it becomes difficult to write a large programs without modular / reusable code. In nodejs we can create modular programs utilising module.exports defining what we expose and compose our program with require.
Try this example:
fileLog.js
function log(string) { require('fs').appendFileSync('log.txt',string); }
module.exports = log;
stdoutLog.js
function log(string) { console.log(string); }
module.exports = log;
program.js
const log = require('./stdoutLog.js')
log('hello world!');
execute
$ node program.js
hello world!
Now try swapping ./stdoutLog.js for ./fileLog.js.
What is the purpose of a module system?
It accomplishes the following things:
Keeps our files from bloating to really big sizes. Having files with e.g. 5000 lines of code in it are usually real hard to deal with during development.
Enforces separation of concerns. Having our code split up into multiple files allows us to have appropriate file names for every file. This way we can easily identify what every module does and where to find it (assuming we made a logical directory structure which is still your responsibility).
Having modules makes it easier to find certain parts of code which makes our code more maintainable.
How does it work?
NodejS uses the CommomJS module system which works in the following manner:
If a file wants to export something it has to declare it using module.export syntax
If a file wants to import something it has to declare it using require('file') syntax
Example:
test1.js
const test2 = require('./test2'); // returns the module.exports object of a file
test2.Func1(); // logs func1
test2.Func2(); // logs func2
test2.js
module.exports.Func1 = () => {console.log('func1')};
exports.Func2 = () => {console.log('func2')};
Other useful things to know:
Modules are getting cached. When you are loading the same module in 2 different files the module only has to be loaded once. The second time a require() is called on the same module the is pulled from the cache.
Modules are loaded in synchronous. This behavior is required, if it was asynchronous we couldn't access the object retrieved from require() right away.
ECMAScript modules - 2022
From Node 14.0 ECMAScript modules are no longer experimental and you can use them instead of classic Node's CommonJS modules.
ECMAScript modules are the official standard format to package JavaScript code for reuse. Modules are defined using a variety of import and export statements.
You can define an ES module that exports a function:
// my-fun.mjs
function myFun(num) {
// do something
}
export { myFun };
Then, you can import the exported function from my-fun.mjs:
// app.mjs
import { myFun } from './my-fun.mjs';
myFun();
.mjs is the default extension for Node.js ECMAScript modules.
But you can configure the default modules extension to lookup when resolving modules using the package.json "type" field, or the --input-type flag in the CLI.
Recent versions of Node.js fully supports both ECMAScript and CommonJS modules. Moreover, it provides interoperability between them.
module.exports
ECMAScript and CommonJS modules have many differences but the most relevant difference - to this question - is that there are no more requires, no more exports, no more module.exports
In most cases, the ES module import can be used to load CommonJS modules.
If needed, a require function can be constructed within an ES module using module.createRequire().
ECMAScript modules releases history
Release
Changes
v15.3.0, v14.17.0, v12.22.0
Stabilized modules implementation
v14.13.0, v12.20.0
Support for detection of CommonJS named exports
v14.0.0, v13.14.0, v12.20.0
Remove experimental modules warning
v13.2.0, v12.17.0
Loading ECMAScript modules no longer requires a command-line flag
v12.0.0
Add support for ES modules using .js file extension via package.json "type" field
v8.5.0
Added initial ES modules implementation
You can find all the changelogs in Node.js repository
let test = function() {
return "Hello world"
};
exports.test = test;