About a year ago I have used Meteor, and now I want to use it again, but many things have changed.
When I follow the Blaze tutorial on Meteor.com, they add imports on top of their files:
import { Meteor } from 'meteor/meteor';
import { Template } from 'meteor/templating';
import { ReactiveDict } from 'meteor/reactive-dict';
I got the app working. But when I comment the imports out, the app keeps working like it should work. Why are these imports needed?
I am still using the regular Javascript, not ES6.
Thanks!
The import statement is used to import functions, objects or primitives that have been exported from an external module, another script, etc.
The name parameter is the name of the object that will receive the exported members. The member parameters specify individual members, while the name parameter imports all of them. name may also be a function if the module exports a single default parameter rather than a series of members. Below are examples to clarify the syntax.
Import an entire module's contents. This inserts myModule into the current scope, containing all the exported bindings from "my-module.js".
For more detail about the different ways we can use import along with their usage, please check this.
They still use the old globals for backwards compatibility. However it is recommended to use the imports so if in some future release they remove the globals your code will still work. You can read more in the appropriate section of the guide.
Ok you know import is to import an exported object from another file already.
The point that you may have missed is that MDG heard the need to stop loading everything by default, or at least to provide a mean to control what is loaded in memory and what is not.
Look for the /imports special directory.
Files in that folder are no longer loaded automatically, but only through import statement.
As for the tutorial, I guess they did not explained this functionality, and because it imports only standard functionalities which are still loaded eagerly for backward compatibility, it does not change anything removing those statements.
Related
When using autoimport feature of nuxt3:
is there any impact (types, performance, bundle-size, tree-shaking, etc..) of using the # alias to import something rather than no import at all?
Or its only purpose is to make imports explicit and maybe help to fix some IDE/linter/ts issues?
Example:
// plugins/vuetify.ts
import { createVuetify, VuetifyOptions } from "vuetify";
import { defineNuxtPlugin, NuxtApp, Plugin } from "#app"; // this line should be optional
export const VuetifyPlugin: Plugin = defineNuxtPlugin((nuxtApp: NuxtApp) => {
const vuetify = createVuetify();
nuxtApp.vueApp.use(vuetify);
});
export default VuetifyPlugin;
I wasn't aware of the # import, do you have a reference for that specifc one?
As you kinda guessed it, there are no direct benefits of making the imports yourself. In the same way that Nuxt does the job for you regarding ref, computed, watch etc, it will try to import most of the other common stuff.
The compiler will scan your file, see what you are using in your template + script part and make the import himself on runtime. It may not guess fully dynamic imports (usually for components based on a dynamic variable for example).
Still, it should work in the exact same way performance-wise.
For the types I know that there could be some limitations (not a full coverage), but since I don't use TS, I'm not well aware of all the details.
Regarding IDEs/code editors, most of the time they will work fine but some of them may require a bit of configuration to work perfectly (since it's implicit, you still need to tell your editor what is happening), otherwise some Linters may complain a bit.
Nuxt's auto import feature is probably based on something really similar (if not identical) to this: https://github.com/antfu/unplugin-auto-import
Hence, you can see in details how this one works to get more explanation.
I would like to use javascript classes with one class per file. It is part of a larger project using eslint. I started with:
/*global CSReport*/
/*global CSManager*/
class CSMain {
constructor() {
this.report = new CSReport();
this.manager = new CSManager(this.report);
}
launchReport(...
}
However, eslint generates an error saying CSMain is defined but never used. This led to the idea of using export and import which seemed better than making everything global (side note: CS in front of main is the old style method to avoid global conflicts)
The question is how to put this together. The release version will be a single (uglified) file, so the class file names will no longer exist when they are all concatenated together in (say) csCompiled.js.
Questions:
Import uses a file name. Should I use the CSCompiled.js name rather than the file names before concatenation?
Do I want a single module or a module for each class?
Do I need to export every class and import every class it uses?
I am not fully sure how angular accesses this code but am thinking to import csMain.
I tried to find an answer to this but am only finding older posts that don't use ecmascript 6 and classes. If an answer to this exists, I am not sure how to get to it.
Background:
The main project uses angular 1. This code is separate for legacy reasons. It is currently written in java using gwt, but we want to move to javascript to remove the reliance on gwt. It is about 30-40 files (classes) total to convert.
The code gets and handles data from the server for report requests. There is a lot of pre-processing done before it is handed back to the rest of the UI.
I have used javascript for an established project using angular, but lack expertise on how to create new projects.
I am trying to use basic javascript for this, so it won't need updating if (for example) we go from angular 1 to the current versions. I do not yet know if this is a good way to do it.
ESLint is complaining because you are not exporting the class you created, therefore, it can't be accessed by other modules. You can fix that with a simple line at the end
export default CSMain;
Import uses a file name. Should I use the CSCompiled.js name rather
than the file names before concatenation?
Use the file name before you compile/transpile/uglify/etc. After that it will all become 1 file and the bundler will take care of that for you.
Do I want a single module or a module for each class?
Completely optional, I like to have 1 class per file and then 1 file for the module (index.js) that lists all classes in that module.
Do I need to export every class and import every class it uses?
Yes, you need to import everything your module will use and export everything that should be public or "importable" for other modules.
I am not fully sure how angular accesses this code but am thinking to import csMain.
It all depends on how you export your file. Make sure to import the same name your module/file is exporting.
I've found at least two ways to import functions in from a module like Ramda for example. There are probably a few more ways to do something very similar like const R = require('ramda');
Option 1 is to import certain functions:
import { cond, T, always, curry, compose } from 'ramda';
Option 2 is to import the whole module like:
import * as R from "ramda";
I would prefer to reference the module from which the function is being called like so:
R.T();
But if the 2nd option is used, does it bring in every Ramda function not just the ones used in a module I'm working in? Are there any impacts on actual memory use, or bandwidth use as far as what gets sent to the browser if option 2 is used?
Is it possible to somehow do this:
// invalid syntax below:
import R { cond, T, always, curry, compose } from 'ramda';
R.T();
My question is kinda related to this one, but it's a bit different
import R (ramda) into typescript .ts file
TL;DR: It does not matter.
import * as … from 'ramda';
import { … } from 'ramda';
will both by default always bring in the complete Ramda module with all its dependencies. All code inside the module would be run, and which syntax was used to reference the exported bindings doesn't matter. Whether you use named or namespaced imports comes down to preference entirely.
What can reduce the file size to download and the used memory is static analysis. After having evaluated the module, the engine can garbage-collect those bindings that are referenced from nowhere. Module namespace objects might make this slightly harder, as anyone with access to the object can access all exports. But still those objects are specified in a way (as immutable) to allow static analysis on their usage and if the only thing you're doing with them is property access with constant names, engines are expected to utilise this fact.
Any size optimisation involves guessing which parts of the module need to be evaluated and which not, and happens in your module bundler (like Rollup or WebPack). This is known as Tree Shaking, dropping parts of the code and entire dependencies when not needed (used by anything that got imported). It should be able to detect which imports you are using regardless of the import style, although it might have to bail out when are doing unusual things with the namespace object (like looping it or using dynamic property access).
To learn about the exact guesses your bundler can make, contact its documentation.
#Bergi is right in his comment, which I think should be the answer. I would also like to point out you can always try things out in Babel to see what it compiles to: click here to see what an example destructuring actually does
So basically even if you destructure just one function from the module, the whole module will be required. In the Babel example I gave, I just extracted Component from the 'react' module, but the compiled code actually just required the whole thing. :)
Adding to #Bergi, Also just for future reference if you want to shed unused functions and import only the desired function, use selective import like below
import isEmpty from 'ramda/src/isEmpty';
This way you can complement it with Webpack and get a better tree shaking. Hope it helps
I assumed at first that it simply means, load the jQuery module and initialize it in a variable called $.
But then, by using Atom with the atom-typescript, I got an error saying that it "Cannot find module 'jquery'". Even though all the code works in the browser, it looks like atom-typescript can't resolve anything looking like import x from y.
Now, looking at ES6 doc, I found out that you import a class/function from a module. The meaning is totally different, and it makes sense with for example this:
import { Component } from 'angular2/core';
But then what does it mean in the case of jQuery?
I am probably mixing different issues in the same one but any explanation would clear this confusion, so thanks a lot in advance :)
The statement import $ from jquery pretty much amounts to dependency injection. Just like one would write import React from 'react' to give oneself access to the React library within a file, so to can one write import $ from jquery. (In case it's throwing you off, the dollar sign is used because jQuery and its methods are accessed using the dollar (a.k.a. jQuery) operator.
As for the errors being thrown, that could be several things:
If you separately installed jQuery as a dependency in your package.json file as well as included a <script> tag from a jQuery CDN, this error will be thrown. If you're usage of jQuery is through NPM, then the import $ from jquery syntax is correct/necessary. If you intend to use jQuery through a CDN (as I would recommend), the import statement is unnecessary. (Since you've included that script tag in your index.html, you have access to jQuery and its library throughout the scope of your application). Do not, however, do both.
Also note that in the case of the import { Component } from 'angular2/core'; statement, something slightly different is going on. Namely, one is importing the named export Component, as per the (AMD specification. You can think of it, in this case, as importing only a part of the larger Angular2 core library when the entire library would be unnecessary.
Just to be sure, check that you have actually given yourself access to jQuery through either a CDN or by installing it as an NPM dependency.
Does using the JavaScript import statement for images, css and others defeat the purpose of import statement which was designed to import only the JS Modules ?
Of course, for now it gets transpiled to ES5 require using webpack. But that same question comes up again. Is it incorrect to use import statement to import images or css or files ?
EDIT:
I like the idea of controlling imports that we can control the assets on build time in such a clean way - The idea that I use the image path to import the image, and
on different environments the image path would contain different values - url or path
this image can be compressed on build time
the JS module importing this image can contain the image dimensions through a custom loader
assets dependency tree is maintained at one place and un-imported items gets chucked away automatically
rebuild time is fast - DX(developer experience) would be good
I guess, this is much better than using any templating, using placeholders in the JS files to inject URLs or paths based on environment during pre-build (webpack).
But using the import statement feels not right to do so in terms of principle or semantics.
This is from Mozilla Developer Network:
The import statement is used to import functions that have been exported from an external module, another script, etc.
From everything I've read on MDN and other sources its purpose is to make a module/script methods and properties available within the current scope it's being imported into.