Whether you’re a web developer, an aspiring programmer, or just curious about the language of the internet, JavaScript is likely to come up in your search. It’s one of the most popular programming languages and it’s used for everything from web development to game development and more.
But where do you start if you want to learn JavaScript? In this blog post, we will cover all the basics of JavaScript and give you all the information you need to get started in using the language. From understanding variables to building functions and more, let’s dive into all things JavaScript!
What is JavaScript?
JavaScript is a programming language that enables you to create dynamic, interactive web pages. JavaScript is used in conjunction with HTML and CSS to create responsive, engaging user interfaces.
JavaScript code can be executed on the client-side, meaning within the web browser, or on the server-side, meaning on the web server. JavaScript code can be embedded directly into HTML code, or it can be stored in external files and referenced from within HTML code.
One of the major benefits of using JavaScript is that it makes web pages more interactive and responsive. For example, you can use JavaScript to validate user input, display dynamic content, and create drop-down menus.
Pros and Cons of JavaScript
JavaScript is a programming language that enables you to create interactive web pages.Pros:1. JavaScript is relatively easy to learn for people with some coding experience.2. It’s widely used, so there’s a large community of developers to help you out if you get stuck.3.
JavaScript code can run on your computer without needing any special software (like a compiler).Cons:1. Some people find the syntax confusing and difficult to read.2. It’s not as fast as some other languages, so it can be slow for large applications.3. It’s not always compatible with all web browsers, so your code may not work for everyone who visits your site.
What Can You Do With JavaScript?
JavaScript is a programming language that can be used to add interactivity to websites. For example, you can use JavaScript to create drop-down menus, form validation, and interactive maps. You can also use it to create games, applications, and tools.
As a web developer, you can use JavaScript to make your website more user-friendly and engaging. You can also use it to improve your website’s performance and speed.
If you’re looking to get into web development, learning JavaScript is a great place to start. It’s a simple language that can be learned relatively easily. And once you know how to code in JavaScript, you’ll be able to create amazing things for the web.
How to Learn JavaScript
JavaScript is a programming language that enables you to create interactive web pages. This tutorial will teach you how to learn JavaScript so that you can make your web pages more interactive.
First, you need to have a basic understanding of HTML and CSS. If you don’t know HTML and CSS, then you should learn them first before trying to learn JavaScript. You can find plenty of resources for learning HTML and CSS on the internet. Once you have a basic understanding of HTML and CSS, then you can move on to learning JavaScript.
There are many resources available for learning JavaScript. You can find plenty of tutorials and examples online. You can also find books about JavaScript at your local bookstore or library. And there are plenty of online courses that you can take to learn JavaScript.
Once you have a basic understanding of the syntax, then you can start writing your own code. There are many good code editors available that will help you write and debug your code. And if you get stuck, there are plenty of resources available to help you out, including Stack Overflow and the Mozilla Developer Network.
When ECMAScript 2015 first introduced ES modules
To standardize the modularity system in JavaScript, it does so by requiring relative or absolute paths to be specified in import statements.
import dayjs from “https://cdn.skypack.dev/[email protected]”; // ES module.
console.log(dayjs(“2019-01-25”).format(“YYYY-MM-DDTHH:mm:ssZ[Z]”));
This is slightly different from how modules work in other popular module systems such as CommonJS, and when using a module bundler like Webpack, which uses a simpler syntax:
const dayjs = require(‘dayjs’) // CommonJS
import dayjs from ‘dayjs’; // network package In these systems, import identifiers are mapped to specific (and versioned) files by the Node.js runtime or related build tools. The user simply applies the bare module identifier (usually the package name) in the import statement and the module resolution problem is solved automatically.
Because developers are already familiar with this way of importing packages from npm, a build step is required to ensure that code written this way will run in the browser. Map import solves this problem. Essentially, it allows import identifiers to be mapped to relative or absolute URLs, which helps control the resolution of modules without applying build steps.
How map import works
<script type="importmap">
{
"imports": {
"dayjs": "https://cdn.skypack.dev/[email protected]",
}
}
</script>
<script type="module">
import dayjs from 'dayjs';
console.log(dayjs('2019-01-25').format('YYYY-MM-DDTHH:mm:ssZ[Z]'));
</script>
Import maps are specified by <script type=”import map”> tags in the HTML document. This script tag must be placed before the first <script type=”module”> tag in the document (preferably in <head> ) so that it is parsed before the module is parsed. Additionally, currently only one import mapping is allowed per document, although there are plans to remove this restriction in the future.
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Inside the script tag, a JSON object is used to specify any necessary mappings for the modules required by the script in the document. A typical import card structure is shown in the following figure:
<script type="importmap">
{
"imports": {
"react": "https://cdn.skypack.dev/[email protected]",
"react-dom": "https://cdn.skypack.dev/react-dom",
"square": "./modules/square.js",
"lodash": "/node_modules/lodash-es/lodash.js"
}
}
</script>
In the import object above, each property corresponds to an association. The left side of the mapping is the name of the imported identifier, while the right side is the relative or absolute URL to which the identifier is mapped. When specifying relative URLs in mappings, make sure they always start with /, ../, or ./. Note that the presence of a package in an import map does not necessarily mean that it will be loaded by the browser. Any module not used by any script on the page will not be loaded by the browser, even if it exists in the import map.
<script type="importmap" src="importmap.json"></script>You can also specify the mapping in an external file, then link to that file using the src attribute (as shown above). If you choose this method, make sure to send the file with its Content-Type header set to “application/importmap+json”. Note that inline methods are recommended for performance reasons, and the examples in the rest of this article are presented this way.
After specifying the mapping, you can use import identifiers in import statements as follows:
<script type="module">
import { cloneDeep } from 'lodash';
const objects = [{ a: 1 }, { b: 2 }];
const deep = cloneDeep(objects);
console.log(deep[0] === objects[0]);
</script>
It is important to note that the mappings in the import map do not affect URLs in places such as the src attribute of the <script> tag. So if you use something like <script src=”/app.js”>, the browser will try to download the literal app.js file at that path, regardless of what’s in the import map.
Assign the specifier to the whole package
In addition to associating identifiers with modules, you can also associate identifiers with packages that contain multiple modules. This is done by using a specifier key and a trailing slash.
<script type="importmap">
{
"imports": {
"lodash/": "/node_modules/lodash-es/"
}
}
</script>
This technique allows you to import any module in the specified path instead of the entire main module, which will download all component modules from the browser.
<script type="module">
import toUpper from 'lodash/toUpper.js';
import toLower from 'lodash/toLower.js';
console.log(toUpper('hello'));
console.log(toLower('HELLO'));
</script>
Dynamic creation of imported maps
Mappings can also be dynamically scripted based on arbitrary conditions, and this feature can be used to conditionally import modules based on feature detection. The following example selects the correct file to import under the lazy loading identifier based on whether the IntersectionObserver API is supported.
<script>
const importMap = {
imports: {
lazyload: 'IntersectionObserver' in window
? './lazyload.js'
: './lazyload-fallback.js',
},
};
const im = document.createElement('script');
im.type = 'importmap';
im.textContent = JSON.stringify(importMap);
document.currentScript.after(im);
</script>
If you want to use this approach, be sure to do this before creating and inserting the import map script tag (as described above), as modifying an already existing import map object has no effect.
Improve script caching capabilities by mapping hashes
A common technique for long-term caching of static files is to use a hash of the file’s content in the filename so that the file remains in the browser cache until the file’s content changes. In this case, the file will be given a new name so that the latest update will appear in the application immediately.
With the traditional approach of bundling scripts, this technique can fail when updating dependencies on which multiple modules depend. This will update all files based on that dependency, forcing the browser to download them again even if a single character of the code has changed.
Import mapping solves this problem by allowing each dependency to be updated separately through a remapping technique. Assuming you need to import methods from a file named post. bundle. 8cb615d12a121f6693aa.js, you can have an import map like this:
<script type="importmap">
{
"imports": {
"post.js": "./static/dist/post.bundle.8cb615d12a121f6693aa.js",
}
}
</script>
instead of writing something like
import { something } from './static/dist/post.bundle.8cb615d12a121f6693aa.js'
you can write the following:
import { something } from 'post.js'
When a file needs to be updated, only the import map needs to be updated. Because the references to their exports haven’t changed, they are still cached in the browser while the updated script is downloaded again based on the updated hash.
<script type="importmap">
{
"imports": {
"post.js": "./static/dist/post.bundle.6e2bf7368547b6a85160.js",
}
}
</script>
Use multiple versions of the same module
It’s easy to request multiple versions of the same package using import maps. All you have to do is use a different import identifier in the map like this:
<script type="importmap">
{
"imports": {
"lodash@3/": "https://unpkg.com/[email protected]/",
"lodash@4/": "https://unpkg.com/[email protected]/"
}
}
</script>
You can also use the same import identifier to refer to different versions of the same package by using scopes. This allows you to change the meaning of import identifiers within a specific scope.
<script type="importmap">
{
"imports": {
"lodash/": "https://unpkg.com/[email protected]/"
},
"scopes": {
"/static/js": {
"lodash/": "https://unpkg.com/[email protected]/"
}
}
}
</script>
With this mapping, all modules in the /static/js path will use the URL https://unpkg.com/[email protected]/ when referencing the lo dash/ specifier in import statements, while other modules will use https: https://unpkg.com/[email protected]/.
Use NPM packages with import maps
As I’ve shown in this article, all production-ready versions of NPM packages that use ES modules are available in your import maps via CDNs like ESM, Un pkg, and Sky pack. Although packages on NPM are not designed for the ES module system and native browser import behavior, services such as Sky pack and ESM can convert them to be usable in import maps. You can use the search bar on the Sky pack home page to find browser-optimized NPM packages that can be used out of the box without messing with build steps.
Programmatic detection import card support
Support for map import can be detected in browsers as long as the HTML Script Element. supports() method is supported. The following code snippet can be used for this:
if (HTMLScriptElement.supports && HTMLScriptElement.supports('importmap')) {
// import maps is supported
}
Legacy Browser Support
Import Maps allows bare module specifiers to be used in the browser without relying on the complex build systems that currently dominate the JavaScript ecosystem, but it is currently not widely supported in web browsers. At the time of this writing, Chrome and Edge browsers version 89 and above have full support, but Firefox, Safari, and some mobile browsers do not support the technology. In order to maintain the use of import maps in such browsers, appropriate poly fills must be used.
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An example of a poly fill that can be used is the ES Module Shims poly fill, which adds support for importing maps and other new module functionality to any browser with basic ES module support (about 94% of browsers). All you need to do is add the es-module-shim script to your HTML file before using the map import script:
<script async src="https://unpkg.com/[email protected]/dist/es-module-shims.js"></script>
In such browsers, you may still get a JavaScript TypeError in the console after inserting the polyfill. This error can be safely ignored as it has no consequences for the user.
Uncaught TypeError: Error resolving module specifier “lodash/toUpper.js”. Relative module specifiers must start with “./”, “../” or “/”.
More poly fills and tools related to import mapping can be found in the GitHub repository.
Conclusion
JavaScript is an incredibly versatile and powerful coding language that can be used to create everything from interactive websites to complex software applications. With its easy-to-use syntax and wide array of features, JavaScript is a great choice for anyone looking to learn programming or expand their current skillset. Whether you’re a beginner just starting out or a seasoned professional looking for the latest technologies, knowing how to use JavaScript will open up many new doors in your journey as a programmer.