jeena/en.javascript.info
1
0
Fork 0
Code Issues Pull requests Projects Packages Wiki Activity Actions

minor fixes

Browse source
This commit is contained in:
Ilya Kantor 2021-05-24 11:18:20 +03:00
parent ffa79a8692
commit a917f9c72d
1 changed files with 16 additions and 5 deletions
Download patch file Download diff file Expand all files Collapse all files

21
1-js/13-modules/01-modules-intro/article.md
View file

@ -81,19 +81,24 @@ Modules always work in strict mode. E.g. assigning to an undeclared variable wil
Each module has its own top-level scope. In other words, top-level variables and functions from a module are not seen in other scripts.
In the example below, two scripts are imported, and `hello.js` tries to use `user` variable declared in `user.js`, and fails (you'll see the error in the console):
In the example below, two scripts are imported, and `hello.js` tries to use `user` variable declared in `user.js`. It fails, because it's a separate module (you'll see the error in the console):
[codetabs src="scopes" height="140" current="index.html"]
Modules are expected to `export` what they want to be accessible from outside and `import` what they need.
Modules should `export` what they want to be accessible from outside and `import` what they need.
So we should import `user.js` into `hello.js` and get the required functionality from it instead of relying on global variables.
- `user.js` should export the `user` variable.
- `hello.js` should import it from `user.js` module.
In other words, with modules we use import/export instead of relying on global variables.
This is the correct variant:
[codetabs src="scopes-working" height="140" current="hello.js"]
In the browser, independent top-level scope also exists for each `<script type="module">`:
In the browser, independent top-level scope also exists for each `<script type="module">`.
Here are two scripts on the same page, both `type="module"`. They don't see each other's top-level variables:
```html run
<script type="module">
@ -108,7 +113,13 @@ In the browser, independent top-level scope also exists for each `<script type="
</script>
```
If we really need to make a window-level global variable, we can explicitly assign it to `window` and access as `window.user`. But that's an exception requiring a good reason.
```smart
In the case of a web browser, we can make a window-level global variable by explicitly assigning it to `window`, e.g. `window.user = "John"`.
Then all scripts will see it.
That said, making such global variables is frowned upon. Please try to avoid them.
```
### A module code is evaluated only the first time when imported