i'm trying to write a library that works in both node.js and the browser. this code uses window.fetch, so i need a polyfill on the server. i would like to write my code something like this:
'use strict'
let fetch
if (ISNODE) {
fetch = require('node-fetch')
} else {
fetch = window.fetch
}
exports.get = params => {
return window.fetch() // and so forth
}
in webpack, it should eliminate the ISNODE tree so that it doesn't try to require('node-fetch') at all.
how do you do this? for now, I'm making window.fetch a global.
You want to use webpack's Define plugin to define constants, then use the Uglify plugin (or something similar) to eliminate dead/unreachable code.
With the Define plugin, define a 'constant' variable for the environment in your build, like IS_SERVER = true. In your conditional, check that constant. Note that this only works when checking variables with boolean values, so it will understand IS_SERVER = true, but not APP_ENV = 'server', for example.
Related
I want to extend a current Node.js module with some global config setting being configured once without breaking current usages of this module.
This is the signature of the module:
const myFunction = function(someOptions) { ... };
module.exports = myFunction;
Usage is
const myFunction = require('myfunction');
const result = myFunction(options);
Now I want to set some options on application startup to be used by the module myfunction whenever being required without breaking current usages of the module myfunction.
If possible, I want to avoid using Node.js global.
Functions in JavaScript are just objects, so you can give them properties. This is a little hacky, but it could certainly work for you:
// greeter.js
function sayHello() {
const message = sayHello.message || "Hi";
console.log(message);
}
module.exports = sayHello;
You can now set the config of this function globally as follows:
const sayHello = require("./greeter.js");
sayHello.message = "S'up dawg";
Any subsequent calls to sayHello() after the code above is executed will use the overridden message. This works because calls to require() are cached, so each time you require(./greeter.js); you're getting back exactly the same function object.
I'd like to override some values at test-time, specifically setting my retries for an http service to 1 (immediate failure, no retries). Our project uses node-config. According to the docs I can override with NODE_CONFIG env variable:
node myapp.js --NODE_CONFIG='{"Customer":{"dbConfig":{"host":"customerdb.prod"}}}'
Well I would prefer to do this in my test, but not for all tests. The code says that you can allow config mutations by setting ALLOW_CONFIG_MUTATIONS.
process.env.ALLOW_CONFIG_MUTATIONS = "true";
const importFresh = require('import-fresh');
importFresh("config");
process.env.NODE_CONFIG = JSON.stringify({httpServices:{integration:{enrich: {retryInterval: 1, retries: 1}}}});
expect(process.env.NODE_CONFIG, 'NODE_CONFIG not set').to.exist();
expect(process.env.NODE_CONFIG, 'NODE_CONFIG not set').to.match(/retryInterval/);
expect(process.env.ALLOW_CONFIG_MUTATIONS, 'ALLOW_CONFIG_MUTATIONS not set').to.equal("true");
const testConfig = require("config");
console.dir(testConfig.get("httpServices.integration.enrich"));
expect(testConfig.get("httpServices.integration.enrich.retryInterval"), 'config value not set to 1').to.equal(1);
Result:
{ url: 'https://internal-**********',
retryInterval: 5000,
retries: 5 }
`Error: config value not set to 1: Expected 5000 to equal specified value: 1`
How do I get this override to work?
(expect is from Hapi.js Code library)
I'm one of the maintainers of node-config. Your bug is that you used require the second time when you should have used importFresh again.
Your first use of "importFresh()" does nothing different than require() would, because it is the first use of require().
After setting some variables, you call require(), which will return the copy of config already generated and cached, ignoring the effects of the environment variables set.
You only needed to use importFresh() once, where you currently use require(). This will cause a "fresh" copy of the config object to be returned, as you expected.
Simply changing config's property worked for me.
For example:
const config = require( 'config' );
config.httpServices.integration.enrich.retryInterval = 1;
// Do your tests...
UPD: Make sure that overrides are done before anyone calls the first config.get(), because the config object is made immutable as soon as any client uses the values via get().
Joining late, but other answers did not fit with the testing standard in my project, so here is what I came up with
TL;DR
Use mocks..
Detailed Answer
node-config uses a function get to get the configuration values.
By mocking the function get you can easily modify any configuration you see fit..
My personal favorite library is sinon
Here is an implementation of a mock with sinon
const config = require('config');
const sinon = require('sinon');
class MockConfig {
constructor () {
this.params = {};
this.sandbox = sinon.sandbox.create();
}
withConfValue (confKey, confValue) {
this.params.confValues[confKey] = confValue;
return this;
}
reset () {
this.params.confValues: {};
return this;
}
restore() {
this.sandbox.restore();
}
apply () {
this.restore(); // avoid duplicate wrapping
this.sandbox.stub(config, 'get').callsFake((configKey) => {
if (this.params.confValues.hasOwnProperty(configKey)) {
return this.params.confValues[configKey];
}
// not ideal.. however `wrappedMethod` approach did not work for me
// https://stackoverflow.com/a/57017971/1068746
return configKey
.split('.')
.reduce((result, item) => result[item], config)
});
}
}
const instance = new MockConfig();
MockConfig.instance = () => instance;
module.exports = MockConfig;
Usage would be
const mockConfig = require('./mock_config').instance();
...
beforeEach(function () {
mockConfig.reset().apply();
})
afterEach(function () {
mockConfig.reset().clear();
})
it('should do something') {
mockConfig.withConfValue('some_topic.some_field.property', someValue);
... rest of the test ...
}
Assumptions
The only assumption this approach makes is that you adhere to node-config way of reading the configuration (using the get function) and not bypass it by accessing fields directly.
It's better to create a development.json, production.json et test.json in your config folder node-config will use it your app configuration.
you just net to set your NODE_ENV to use the specific file.
Hope it helps :)
I am playing around and learning about vows with a personal project. This is a small client side library, with testing done in vows. Therefore, I must build and test a file that is written like this:
(function(exports) {
var module = export.module = { "version":"0.0.1" };
//more stuff
})(this);
In my testing (based off of science.js, d3, etc.) requires that module like so:
require("../module");
I continued to get a "module not defined error" when trying to run the tests, so I went to a repl and ran:
require("../module")
and it returned:
{ module: { version: "0.0.1" } }
I realize I could do something like:
var module = require("../module").module;
but feel like I am creating a problem by doing it that way, especially since the libraries that I based this project on are doing it in the format I described.
I would like for my project to behave similar to those which I based it off of, where:
require("../module");
creates a variable in this namespace:
module.version; //is valid.
I have seen this in a variety of libraries, and I am following the format and thought process to the T but believe I might be missing something about require behavior I don't know about.
There is no problem creating it this way. Modules define what they return in the module.exports object. By the way, you don't actually need self executing functions (SEF), there is no global leakage like in browsers :-)
Examples
module1.js:
module.exports = {
module: { 'version': '0.1.1' }
};
main.js:
var module1 = require( './module1.js' );
// module1 has what is exported in module1.js
Once you've understood how this works, you can easily export the version number right away if you want to:
module1.js:
module.exports = '0.1.1';
main.js:
var module1 = require( './module1.js' );
console.log( module1 === '0.1.1' ); // true
Or if you want some logic, you can easily extend your module1.js file like this:
module.exports = ( function() {
// some code
return version;
} () ); // note the self executing part :-)
// since it's self executed, the exported part
// is what's returned in the SEF
Or, as many modules do, if you want to export some utility functions (and keep others "private"), you could do it like this:
module.exports = {
func1: function() {
return someFunc();
},
func2: function() {},
prop: '1.0.0'
};
// This function is local to this file, it's not exported
function someFunc() {
}
So, in main.js:
var module1 = require( './module1.js' );
module1.func1(); // works
module1.func2(); // works
module1.prop; // "1.0.0"
module1.someFunc(); // Reference error, the function doesn't exist
Your special case
About your special case, I wouldn't recommend doing it like they're doing.
If you look here: https://github.com/jasondavies/science.js/blob/master/science.v1.js
You see that they're not using the var keyword. So, they're creating a global variable.
This is why they can access it once they require the module defining the global variable.
And by the way, the exports argument is useless in their case. It's even misleading, since it actually is the global object (equivalent of window in browsers), not the module.exports object (this in functions is the global object, it'd be undefined if strict mode were enabled).
Conclusion
Don't do it like they're doing, it's a bad idea. Global variables are a bad idea, it's better to use node's philosophy, and to store the required module in a variable that you reuse.
If you want to have an object that you can use in client side and test in node.js, here is a way:
yourModule.js:
// Use either node's export or the global object in browsers
var global = module ? module.exports : window.yourModule;
( function( exports ) {
var yourModule = {};
// do some stuff
exports = yourModule;
} ( global ) );
Which you can shorten to this in order to avoid creating the global variable:
( function( exports ) {
var yourModule = {};
// do some stuff
exports = yourModule;
} ( module ? module.exports : window.yourModule ) );
This way, you can use it like this on the client-side:
yourModule.someMethod(); // global object, "namespace"
And on the server side:
var yourModule = require( '../yourModule.js' );
yourModule.someMethod(); // local variable :-)
Just FYI, .. means "parent directory". This is the relative path of where to get the module. If the file were in the same directory, you'd use ..
How can I include a file, which contains classes definitions in my server.js file?
I don't want to use module.exports because I want to use this file in my client javascript code too.
Thank you!
If you want the module's contents to be available outside the scope of the file you have to use module.exports. Making the file also work in a browser just requires you to do some extra if/elses
For instance:
var self = {};
// Browser?
if(instanceof window !== 'undefined')
{
window['my_module_name'] = self;
}
// Otherwise assume Node.js
else
{
module.exports = self;
}
// Put the contents of this module in self
// For instance:
self.some_module_function = function() {
// Do stuff
}
Now if you're in Node.js you can reach the function like this:
my_module = require('my_module_name');
my_module.some_module_function(58);
Or if you're in a browser you can just call it directly since it's global:
my_module.some_module_function(58);
Otherwise I can recommend Stitch.js which allows you to develop JavaScript code using the CommonJS style require and modules, then compile it to also run in the browser with no code changes.
Require.js also allows for this type of functionality.
Here's another SO question about using the same code in node and browsers:
how to a use client js code in nodejs
maybe this question is a little silly, but is it possible to load multiple .js files with one require statement? like this:
var mylib = require('./lib/mylibfiles');
and use:
mylib.foo(); //return "hello from one"
mylib.bar(): //return "hello from two"
And in the folder mylibfiles will have two files:
One.js
exports.foo= function(){return "hello from one";}
Two.js
exports.bar= function(){return "hello from two";}
I was thinking to put a package.json in the folder that say to load all the files, but I don't know how. Other aproach that I was thinking is to have a index.js that exports everything again but I will be duplicating work.
Thanks!!
P.D: I'm working with nodejs v0.611 on a windows 7 machine
First of all using require does not duplicate anything. It loads the module and it caches it, so calling require again will get it from memory (thus you can modify module at fly without interacting with its source code - this is sometimes desirable, for example when you want to store db connection inside module).
Also package.json does not load anything and does not interact with your app at all. It is only used for npm.
Now you cannot require multiple modules at once. For example what will happen if both One.js and Two.js have defined function with the same name?? There are more problems.
But what you can do, is to write additional file, say modules.js with the following content
module.exports = {
one : require('./one.js'),
two : require('./two.js'),
/* some other modules you want */
}
and then you can simply use
var modules = require('./modules.js');
modules.one.foo();
modules.two.bar();
I have a snippet of code that requires more than one module, but it doesn't clump them together as your post suggests. However, that can be overcome with a trick that I found.
function requireMany () {
return Array.prototype.slice.call(arguments).map(function (value) {
try {
return require(value)
}
catch (event) {
return console.log(event)
}
})
}
And you use it as such
requireMany("fs", "socket.io", "path")
Which will return
[ fs {}, socketio {}, path {} ]
If a module is not found, an error will be sent to the console. It won't break the programme. The error will be shown in the array as undefined. The array will not be shorter because one of the modules failed to load.
Then you can bind those each of those array elements to a variable name, like so:
var [fs, socketio, path] = requireMany("fs", "socket.io", "path")
It essentially works like an object, but assigns the keys and their values to the global namespace. So, in your case, you could do:
var [foo, bar] = requireMany("./foo.js", "./bar.js")
foo() //return "hello from one"
bar() //return "hello from two"
And if you do want it to break the programme on error, just use this modified version, which is smaller
function requireMany () {
return Array.prototype.slice.call(arguments).map(require)
}
Yes, you may require a folder as a module, according to the node docs. Let's say you want to require() a folder called ./mypack/.
Inside ./mypack/, create a package.json file with the name of the folder and a main javascript file with the same name, inside a ./lib/ directory.
{
"name" : "mypack",
"main" : "./lib/mypack.js"
}
Now you can use require('./mypack') and node will load ./mypack/lib/mypack.js.
However if you do not include this package.json file, it may still work. Without the file, node will attempt to load ./mypack/index.js, or if that's not there, ./mypack/index.node.
My understanding is that this could be beneficial if you have split your program into many javascript files but do not want to concatenate them for deployment.
You can use destructuring assignment to map an array of exported modules from require statements in one line:
const requires = (...modules) => modules.map(module => require(module));
const [fs, path] = requires('fs', 'path');
I was doing something similar to what #freakish suggests in his answer with a project where I've a list of test scripts that are pulled into a Puppeteer + Jest testing setup. My test files follow the naming convention testname1.js - testnameN.js and I was able use a generator function to require N number of files from the particular directory with the approach below:
const fs = require('fs');
const path = require('path');
module.exports = class FilesInDirectory {
constructor(directory) {
this.fid = fs.readdirSync(path.resolve(directory));
this.requiredFiles = (this.fid.map((fileId) => {
let resolvedPath = path.resolve(directory, fileId);
return require(resolvedPath);
})).filter(file => !!file);
}
printRetrievedFiles() {
console.log(this.requiredFiles);
}
nextFileGenerator() {
const parent = this;
const fidLength = parent.requiredFiles.length;
function* iterate(index) {
while (index < fidLength) {
yield parent.requiredFiles[index++];
}
}
return iterate(0);
}
}
Then use like so:
//Use in test
const FilesInDirectory = require('./utilities/getfilesindirectory');
const StepsCollection = new FilesInDirectory('./test-steps');
const StepsGenerator = StepsCollection.nextFileGenerator();
//Assuming we're in an async function
await StepsGenerator.next().value.FUNCTION_REQUIRED_FROM_FILE(someArg);