The JavaScript import map is a powerful feature in web development that provides developers with granular control over how module specifiers are resolved by the browser when importing JavaScript modules. At its core, JavaScript import map is a JSON object that serves as a centralized registry for module mappings, allowing developers to define custom mappings for modules and their dependencies.
With an import map, developers can specify the exact URLs where modules should be loaded from, allowing them to easily switch between different versions of modules or use modules hosted on a content delivery network (CDN). This provides greater flexibility in managing module dependencies and can lead to faster load times for web applications.
Import maps also help to address some of the challenges associated with traditional module loading approaches, such as the need to manually specify URLs for every module. By centralizing module mappings in a single JSON object, developers can streamline the process of managing module dependencies and reduce the amount of code needed to import modules.
Overall, the JavaScript import map is an important feature in modern web development that provides developers with greater control over how module dependencies are resolved and loaded by the browser. As web applications continue to become more complex, the import map will undoubtedly play an increasingly important role in managing dependencies and improving performance.
Module Scripts
Module scripts are a relatively new development in web development that provide web pages with a powerful tool to manage JavaScript imports. They are essentially JavaScript files that have been augmented with the “module” keyword, which designates them as a module script. This allows them to be loaded and executed asynchronously by the web browser, with support for dynamic import and export statements.
One of the most exciting features of module scripts is their potential to enable web developers to dispense with their build system. This is because module scripts provide a standardized and declarative approach to managing dependencies, which means that web developers can simply list the modules they need in their HTML file and let the web browser take care of the rest.
This approach is a departure from the traditional way of managing JavaScript imports, which involves using a build system to bundle and optimize the code for production. While build systems have proven to be effective in managing complex web applications, they can also be cumbersome and time-consuming to set up and maintain. With module scripts, web developers can potentially streamline their development process and reduce the complexity of their code-base.
Overall, module scripts represent an exciting development in web development that has the potential to simplify the management of JavaScript imports and reduce the complexity of web applications. As the technology continues to evolve, it will be interesting to see how web developers incorporate module scripts into their development workflows and whether they truly provide a viable alternative to build systems.
JavaScript Import Maps examples
<script type="importmap">
{
"imports": {
"dayjs": "https://cdn.skypack.dev/dayjs@1.10.7",
}
}
</script>
<script type="module">
import dayjs from 'dayjs';
console.log(dayjs('2023-04-05').format('mm.DD.YYYYTHH:mm:ssZ[Z]'));
</script>
The import map is a key concept in web development that allows developers to specify how their web page imports and resolves module dependencies. It is defined through the <script type=”importmap”> tag in an HTML document and is used to map module specifiers to actual URLs, essentially providing a central registry of modules that can be accessed throughout the document.
To ensure that the import map is properly parsed and utilized, it must be placed before the first <script type=”module”> tag in the document, preferably in the <head> section. This is because module resolution is carried out during the parsing of the HTML document, and the import map must be parsed before any modules are loaded.
It is important to note that only one import map is currently allowed per document. However, there are plans to remove this limitation in the future, allowing developers to have multiple import maps if necessary.
The import map itself is specified as a JSON object within the <script type=”importmap”> tag. This object contains key-value pairs, where the key represents the module specifier and the value represents the URL to the actual module. For example, the following code snippet shows an import map that maps the module specifier “lodash” to the URL “https://cdn.example.com/lodash.js“:
<script type="importmap">
{
"imports": {
"lodash": "https://cdn.example.com/lodash.js"
}
}
</script>
By specifying an import map, developers can ensure that their web page’s module dependencies are resolved correctly and efficiently. They can also simplify their code-base by centralizing module mapping and avoiding the need to hard-code URLs throughout their code. As such, the import map is an important tool in modern web development that helps developers manage their code and streamline their development process.
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 that is not utilized by a script on the page will not be loaded by the browser, even if it is present in the import map.
You can also specify your JavaScript import map in an external file:
<script type="importmap" src="../js/importmap.json"></script>
JavaScript Import Maps Browser Support
Most of browsers already support this feature…
Using the <script type="importmap"> tag and the import keyword provides several benefits over older, non-modular approaches to JavaScript development. It allows you to clearly and explicitly specify the external modules your code depends on, which makes it easier to understand and maintain your code. Overall, using ES modules with the <script type="importmap"> tag is a modern and powerful way to include and reuse JavaScript code in web applications.
You can check if the feature is supported with:
if (HTMLScriptElement.supports && HTMLScriptElement.supports('importmap')) {
// yay
}
Are you excited to use this feature in your next project? Please share your thoughts in the comments below.