A Handy Guide to Using Dynamic Import in JavaScript
Tags: javascript, typescript, webdev, beginners
Published: 2024-04-25 03:00:00

## Introduction
In JavaScript, when we import a file, the process usually happens synchronously, known as static import. However, as our applications grow, this synchronous loading can lead to slower initial page loads due to larger JavaScript bundles. Moreover, there are times when imports are necessary only under specific circumstances, leading to unnecessary loading times for users who might not even utilize those features.


## Details
Instead of burdening all users with unnecessary imports, dynamic imports come to the rescue. They allow us to load modules or files only when they are needed, thus improving performance and user experience.

Dynamic imports are invoked using the import() function and return a promise. When using default exports, the exported data can be accessed through the default field, while other data can be accessed through fields with matching names.

Here's how you can use dynamic imports:
```ts
import("ramda").then(module => {
  const moduleDefault = module.default;
  console.log(moduleDefault);
});

import("./utility.js").then(module => {
  const DefaultFunction = module.default;
  const exportFunction = module.exportFunction;
  console.log(DefaultFunction, exportFunction);
});
```

An example of practical use is loading a chat box library only when a user clicks a contact button:
```ts
const contactBtn = document.querySelector("#button");
contactBtn.addEventListener("click", () => {
    import("chat-box").then(module => {
        module.load(); // or perform any desired action
    });
});
```

It's worth noting that directly performing a static import inside an event listener callback is invalid.
```ts
const contactBtn = document.querySelector("#button");
contactBtn.addEventListener("click", () => {
    import {init} from "chat-box" // not work
    module.load();
});
```

### Example with async/await
Since dynamic import returns a promise, you can use the async/await syntax.
```ts
const contactBtn = document.querySelector("#button");
contactBtn.addEventListener("click", async () => {
    const module = await import("chat-box");
    module.load();
});
```

### Example with destructuring
You can also use object destructuring here because it returns an object. For example: we can destructure the load function from the module object:
```ts
const contactBtn = document.querySelector("#button");
contactBtn.addEventListener("click", async () => {
    const {load} = await import("chat-box");
    load();
});
```

### Error Handling
Don't forget error handling! Dynamic imports may throw errors due to network conditions or other issues. Therefore, it's essential to use try/catch blocks or catch promises to handle potential errors gracefully.
```ts
try {
  const module = await import("chat-box");
} catch(e) {
  console.error(e)
}

// or
import("chat-box").catch(console.error)
```

## Conclusion
Dynamic imports in JavaScript offer a solution to the synchronous loading bottleneck of static imports. By using the import() function, we can load modules or files on demand, enhancing performance and optimizing user experience. Remember, always handle errors when working with dynamic imports to ensure smooth functionality.

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