I understand eval string-to-function is impossible to use on the browsers' application programming interfaces, but there must be another strategy to use third party dependencies without node.js on v8 engine, given Cloudflare does it in-house, unless they disable the exclusive method by necessity or otherwise on their edge servers for Workers. I imagine I could gather the AST of the commonjs module, as I was able to by rollup watch, but what might the actual steps be, by tooling? I mention AMD for it seems to rely on string-to-function (to-which I've notice Mozilla MDN says nothing much about it).
I have been exploring the require.js repositories, and they either use eval or AST
function DEFNODE(type, props, methods, base) {
if (arguments.length < 4) base = AST_Node;
if (!props) props = [];
else props = props.split(/\s+/);
var self_props = props;
if (base && base.PROPS) props = props.concat(base.PROPS);
var code = "return function AST_" + type + "(props){ if (props) { ";
for (var i = props.length; --i >= 0; ) {
code += "this." + props[i] + " = props." + props[i] + ";";
}
var proto = base && new base();
if ((proto && proto.initialize) || (methods && methods.initialize))
code += "this.initialize();";
code += "}}";
//constructor
var cnstor = new Function(code)();
if (proto) {
cnstor.prototype = proto;
cnstor.BASE = base;
}
if (base) base.SUBCLASSES.push(cnstor);
cnstor.prototype.CTOR = cnstor;
cnstor.PROPS = props || null;
cnstor.SELF_PROPS = self_props;
cnstor.SUBCLASSES = [];
if (type) {
cnstor.prototype.TYPE = cnstor.TYPE = type;
}
if (methods)
for (i in methods)
if (HOP(methods, i)) {
if (/^\$/.test(i)) {
cnstor[i.substr(1)] = methods[i];
} else {
cnstor.prototype[i] = methods[i];
}
}
//a function that returns an object with [name]:method
cnstor.DEFMETHOD = function (name, method) {
this.prototype[name] = method;
};
if (typeof exports !== "undefined") exports[`AST_${type}`] = cnstor;
return cnstor;
}
var AST_Token = DEFNODE(
"Token",
"type value line col pos endline endcol endpos nlb comments_before file raw",
{},
null
);
https://codesandbox.io/s/infallible-darwin-8jcl2k?file=/src/mastercard-backbank/uglify/index.js
https://www.youtube.com/watch?v=EF7UW9HxOe4
Is it possible to make a C++ addon just to add a default object for
node.js named exports or am I Y’ing up the wrong X
'.so' shared library for C++ dlopen/LoadLibrary (or #include?)
“I have to say that I'm amazed that there is code out there that loads one native addon from another native addon! Is it done by acquiring and then calling an instance of the require() function, or perhaps by using uv_dlopen() directly?”
N-API: An api for embedding Node in applications
"[there is no ]napi_env[ just yet]."
node-api: allow retrieval of add-on file name - Missing module in Init
Andreas Rossberg - is AST parsing, or initialize node.js abstraction for native c++, enough?
v8::String::NewFromUtf8(isolate, "Index from C++!");
Rising Stack - Node Source
"a macro implicit" parameter - bridge object between
C++ and JavaScript runtimes
extract a function's parameters and set the return value.
#include <nan.h>
int build () {
NAN_METHOD(Index) {
info.GetReturnValue().Set(
Nan::New("Index from C++!").ToLocalChecked()
);
}
}
// Module initialization logic
NAN_MODULE_INIT(Initialize) {
/*Export the `Index` function
(equivalent to `export function Index (...)` in JS)*/
NAN_EXPORT(target, Index);
}
New module "App" Initialize function from NAN_MODULE_INIT (an atomic?-macro)
"__napi_something doesn't exist."
"node-addon-API module for C++ code (N-API's C code's headers)"
NODE_MODULE(App, Initialize);
Sep 17, 2013, 4:42:17 AM to v8-u...#googlegroups.com "This comes up
frequently, but the answer remains the same: scrap the idea. ;)
Neither the V8 parser nor its AST are designed for external
interfacing. In particular (1) V8's AST does not necessarily reflect
JavaScript syntax 1-to-1, (2) we change it all the time, and (3) it
depends on various V8 internals. And since all these points are
important for V8, don't expect the situation to change.
/Andreas"
V8 c++: How to import module via code to script context (5/28/22, edit)
"The export keyword may only be used in a module interface unit.
The keyword is attached to a declaration of an entity, and causes that
declaration (and sometimes the definition) to become visible to module
importers[ - except for] the export keyword in the module-declaration, which is just a re-use of the keyword (and does not actually “export” ...entities)."
SyntheticModule::virtual
ScriptCompiler::CompileModule() - "Corresponds to the ParseModule abstract operation in the ECMAScript specification."
Local<Function> foo_func = ...;//external
Local<Module> module = Module::CreateSyntheticModule(
isolate, name,
{String::NewFromUtf8(isolate, "foo")},
[](Local<Context> context, Local<Module> module) {
module->SetSyntheticModuleExport(
String::NewFromUtf8(isolate, "foo"), foo_func
);
});
Context-Aware addons from node.js' commonjs modules
export module index;
export class Index {
public:
const char* app() {
return "done!";
}
};
import index;
import <iostream>;
int main() {
std::cout << Index().app() << '\n';
}
node-addon-api (new)
native abstractions (old)
"Thanks to the crazy changes in V8 (and some in Node core), keeping native addons compiling happily across versions, particularly 0.10 to 0.12 to 4.0, is a minor nightmare. The goal of this project is to store all logic necessary to develop native Node.js addons without having to inspect NODE_MODULE_VERSION and get yourself into a macro-tangle[ macro = extern atomics?]."
Scope Isolate (v8::Isolate), variable Local (v8::Local)
typed_array_to_native.cc
"require is part of the Asynchronous Module Definition AMD API[, without "string-to-function" eval/new Function()],"
node.js makes objects, for it is written in C++.
"According to the algorithm, before finding
./node_modules/_/index.js, it tried looking for express in the
core Node.js modules. This didn’t exist, so it looked in node_modules,
and found a directory called _. (If there was a
./node_modules/_.js, it would load that directly.) It then
loaded ./node_modules/_/package.json, and looked for an exports
field, but this didn’t exist. It also looked for a main field, but
this didn’t exist either. It then fell back to index.js, which it
found. ...require() looks for node_modules in all of the parent directories of the caller."
But java?
I won't accept this answer until it works, but this looks promising:
https://developer.oracle.com/databases/nashorn-javascript-part1.html
If not to run a jar file or something, in the Worker:
https://github.com/nodyn/jvm-npm
require and build equivalent in maven, first, use "dist/index.js".
Specifically: [ScriptEngineManager][21]
https://stackoverflow.com/a/15787930/11711280
Actually: js.commonjs-require experimental
https://docs.oracle.com/en/graalvm/enterprise/21/docs/reference-manual/js/Modules/
Alternatively/favorably: commonjs builder in C (v8 and node.js)
https://www.reddit.com/r/java/comments/u7elf4/what_are_your_thoughts_on_java_isolates_on_graalvm/
Here I will explore v8/node.js src .h and .cc for this purpose
https://codesandbox.io/s/infallible-darwin-8jcl2k?file=/src/c.cpp
I'm curious why there is near machine-level C operability in Workers if not to use std::ifstream, and/or build-locally, without node.js require.
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;
I'm working on some repo. And add refactoring to extract some functionality into class
The question is -- I prefer to use passing dependencies from outside (DI). But I see that it's not common pattern for node.js application.
So the question - is there any good examples ( links to repos ) where guys use DI for providing dependencies.
The opposite opinion is -- "We always can use proxyquire module to mock dependencies"
P.S
example for code I propose is
// use
const inst = new Cls(getDep1(), getDep2());
// where getDep1 / getDep2 provide dependencies from side modules
instead of
//Cls
const dep1 = require('dep1');
const dep2 = require('dep2');
module.exports = function Cls() {
// deps usage
}
// and
const inst = new Cls();
The question is about arguments in node.js related projects
Your example is about as clear as it gets. If you want to configure a stub/mock in a test for a class dependency without using proxyquire or mockery or some other require patcher, then you have to provide another point of entry into your code.
you could explicitly use DI like in your example:
function Cls(dep1, dep2) {
this.dep1 = dep1;
this.dep2 = dep2;
}
Which could live off by itself, then your calling code would be responsible for importing your class, configuring its dependencies, and instantiating it correctly. That way your Cls is isolated and unit testable itself.
You could also expose the dependencies that need to be handled as public properties:
const dep1 = require('dep1');
const dep2 = require('dep2');
module.exports = function Cls() {
this.dep1 = dep1;
this.dep2 = dep2;
}
That could allow the module that Cls is defined in to also contain the code that associates it with its deps, while still allowing your unit tests to easily configure Cls with mock/stub objects. This relies on requires to be side effect free :(
var cls = new Cls();
cls.dep1 = new SomeStub();
cls.dep2 = new SomeStub();
cls.exercise();
When I use pulp build -O -t html/main.js and then pulp build -O -I test -m Test.Main -t html/testmain.js (i.e. building main and test) I get two different js output. In the former case, the format is
// Generated by psc-bundle 0.8.2.0
var PS = { };
(function(exports) {
// Generated by psc version 0.8.2.0
"use strict";
var Prelude = require("../Prelude");
var Control_Monad_Eff = require("../Control.Monad.Eff");
exports["main"] = main;
})(PS["Main"] = PS["Main"] || {});
PS["Main"].main();
Please note the require. In the latter case, the require is not in place at all
// Generated by psc-bundle 0.8.2.0
var PS = { };
(function(exports) {
/* global exports */
"use strict";
exports.concatArray = function (xs) {
return function (ys) {
return xs.concat(ys);
};
};
exports.showNumberImpl = function (n) {
/* jshint bitwise: false */
return n === (n | 0) ? n + ".0" : n.toString();
};
})(PS["Prelude"] = PS["Prelude"] || {});
(function(exports) {
// Generated by psc version 0.8.2.0
"use strict";
var $foreign = PS["Prelude"];
var Semigroupoid = function (compose) {
this.compose = compose;
};
Both examples are shorten, but the point is that require is used in the first time, while not used in the second time.
The issue is that I am not able to run the version using require in the browser due to this error
ReferenceError: require is not defined
When I included require.js into page, I got this error
Error: Module name "../Prelude" has not been loaded yet for context: _. Use require([])
http://requirejs.org/docs/errors.html#notloaded
Thus my question is, what can be done to run the first case in browser.
My guess would be that this comes from running builds with different --require-path options; once with the old default, which was an empty string, and once with ../. This would lead to psc-bundle not realising it needed to include Prelude and Control.Monad.Eff properly in the first case. psc-bundle should replace those require calls with references to the other modules, so that the code works in browsers.
There are a few different ways this can happen, and the compiler has been updated now in a way that should make the probability of this happening again much lower, so I wouldn't spend too much time worrying about exactly how this has occurred.
If none of the above makes any sense to you, don't worry; I think you just need to do the following to fix this:
Update to the latest version of psc (0.8.3 changed the --require-path default to ../, so any version after 0.8.3 should do, but you will want the latest version in most cases)
Delete your output directory
Compile everything again.
You probably need to use the --browserify option to build the first case for the browser.
After following instructions on the emscripten wiki I have managed to compile a small C library. This resulted in an a.out.js file.
I was assuming that to use functions from this library (within node.js) something like this would have worked:
var lib = require("./a.out.js");
lib.myFunction('test');
However this fails. Can anyone help or point me to some basic tutorial related to this?
Actually, all the functions are already exported. Generated JavaScript contains following lines:
var ENVIRONMENT_IS_NODE = typeof process === 'object' && typeof require === 'function';
// …
if (ENVIRONMENT_IS_NODE) {
// …
module['exports'] = Module;
}
If you got a function called my_fun in your C code, then you'll have Module._my_fun defined.
There are some problems with this approach, though.
Optimizer may remove or rename some functions, so always specify them passing -s EXPORTED_FUNCTIONS="['_main','_fun_one','_fun_two']". Function signatures in C++ are bit mangled, so it's wise to extern "C" { … } the ones which you want to export.
Furthermore, such a direct approach requires JS to C type conversions. You may want to hide it by adding yet another API layer in file added attached with --pre-js option:
var Module = {
my_fun: function(some_arg) {
javascript to c conversion goes here;
Module._my_fun(converted_arg) // or with Module.ccall
}
}
Module object will be later enhanced by all the Emscripten-generated goodies, so don't worry that it's defined here, not modified.
Finally, you will surely want to consider Embind which is a mechanism for exposing nice JavaScript APIs provided by Emscripten. (Requires disabling newest fastcomp backend.)
The problem here is that your a.out.js file is going to look like this
function myFunction() {
...
}
Not like this
function myFunction() {
...
}
exports.myFunction = myFunction;
You need to write a build script that lists the tokens you want to publically export from each C program and appends exports.<token> = <token>;\n to the end of your file for each token.