mirror of
https://github.com/denoland/deno.git
synced 2024-10-31 09:14:20 -04:00
110 lines
3.8 KiB
Markdown
110 lines
3.8 KiB
Markdown
# Linking to third party code
|
|
|
|
In the [Getting Started](./getting_started.md) section, we saw Deno could
|
|
execute scripts from URLs. Like browser JavaScript, Deno can import libraries
|
|
directly from URLs. This example uses a URL to import an assertion library:
|
|
|
|
**test.ts**
|
|
|
|
```ts
|
|
import { assertEquals } from "https://deno.land/std@$STD_VERSION/testing/asserts.ts";
|
|
|
|
assertEquals("hello", "hello");
|
|
assertEquals("world", "world");
|
|
|
|
console.log("Asserted! ✓");
|
|
```
|
|
|
|
Try running this:
|
|
|
|
```shell
|
|
$ deno run test.ts
|
|
Compile file:///mnt/f9/Projects/github.com/denoland/deno/docs/test.ts
|
|
Download https://deno.land/std@$STD_VERSION/testing/asserts.ts
|
|
Download https://deno.land/std@$STD_VERSION/fmt/colors.ts
|
|
Download https://deno.land/std@$STD_VERSION/testing/diff.ts
|
|
Asserted! ✓
|
|
```
|
|
|
|
Note that we did not have to provide the `--allow-net` flag for this program,
|
|
and yet it accessed the network. The runtime has special access to download
|
|
imports and cache them to disk.
|
|
|
|
Deno caches remote imports in a special directory specified by the `DENO_DIR`
|
|
environment variable. It defaults to the system's cache directory if `DENO_DIR`
|
|
is not specified. The next time you run the program, no downloads will be made.
|
|
If the program hasn't changed, it won't be recompiled either. The default
|
|
directory is:
|
|
|
|
- On Linux/Redox: `$XDG_CACHE_HOME/deno` or `$HOME/.cache/deno`
|
|
- On Windows: `%LOCALAPPDATA%/deno` (`%LOCALAPPDATA%` = `FOLDERID_LocalAppData`)
|
|
- On macOS: `$HOME/Library/Caches/deno`
|
|
- If something fails, it falls back to `$HOME/.deno`
|
|
|
|
## FAQ
|
|
|
|
### How do I import a specific version of a module?
|
|
|
|
Specify the version in the URL. For example, this URL fully specifies the code
|
|
being run: `https://unpkg.com/liltest@0.0.5/dist/liltest.js`.
|
|
|
|
### It seems unwieldy to import URLs everywhere.
|
|
|
|
> What if one of the URLs links to a subtly different version of a library?
|
|
|
|
> Isn't it error prone to maintain URLs everywhere in a large project?
|
|
|
|
The solution is to import and re-export your external libraries in a central
|
|
`deps.ts` file (which serves the same purpose as Node's `package.json` file).
|
|
For example, let's say you were using the above assertion library across a large
|
|
project. Rather than importing
|
|
`"https://deno.land/std@$STD_VERSION/testing/asserts.ts"` everywhere, you could
|
|
create a `deps.ts` file that exports the third-party code:
|
|
|
|
**deps.ts**
|
|
|
|
```ts
|
|
export {
|
|
assert,
|
|
assertEquals,
|
|
assertStrContains,
|
|
} from "https://deno.land/std@$STD_VERSION/testing/asserts.ts";
|
|
```
|
|
|
|
And throughout the same project, you can import from the `deps.ts` and avoid
|
|
having many references to the same URL:
|
|
|
|
```ts
|
|
import { assertEquals, runTests, test } from "./deps.ts";
|
|
```
|
|
|
|
This design circumvents a plethora of complexity spawned by package management
|
|
software, centralized code repositories, and superfluous file formats.
|
|
|
|
### How can I trust a URL that may change?
|
|
|
|
By using a lock file (with the `--lock` command line flag), you can ensure that
|
|
the code pulled from a URL is the same as it was during initial development. You
|
|
can learn more about this
|
|
[here](./linking_to_external_code/integrity_checking.md).
|
|
|
|
### But what if the host of the URL goes down? The source won't be available.
|
|
|
|
This, like the above, is a problem faced by _any_ remote dependency system.
|
|
Relying on external servers is convenient for development but brittle in
|
|
production. Production software should always vendor its dependencies. In Node
|
|
this is done by checking `node_modules` into source control. In Deno this is
|
|
done by pointing `$DENO_DIR` to some project-local directory at runtime, and
|
|
similarly checking that into source control:
|
|
|
|
```shell
|
|
# Download the dependencies.
|
|
DENO_DIR=./deno_dir deno cache src/deps.ts
|
|
|
|
# Make sure the variable is set for any command which invokes the cache.
|
|
DENO_DIR=./deno_dir deno test src
|
|
|
|
# Check the directory into source control.
|
|
git add -u deno_dir
|
|
git commit
|
|
```
|