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137 lines
2.8 KiB
Markdown
137 lines
2.8 KiB
Markdown
# Deno Node compatibility
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This module is meant to have a compatibility layer for the
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[NodeJS standard library](https://nodejs.org/docs/latest-v12.x/api/).
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**Warning**: Any function of this module should not be referred anywhere in the
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deno standard library as it's a compatibility module.
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## Supported Builtins
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- [ ] assert
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- [x] buffer
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- [ ] child_process
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- [ ] cluster
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- [ ] console
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- [ ] crypto
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- [ ] dgram
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- [ ] dns
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- [x] events
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- [x] fs _partly_
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- [ ] http
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- [ ] http2
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- [ ] https
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- [x] module
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- [ ] net
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- [x] os _partly_
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- [x] path
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- [ ] perf_hooks
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- [x] process _partly_
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- [x] querystring
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- [ ] readline
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- [ ] repl
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- [ ] stream
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- [ ] string_decoder
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- [ ] sys
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- [x] timers
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- [ ] tls
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- [ ] tty
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- [ ] url
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- [x] util _partly_
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- [ ] ~~v8~~ _can't implement_
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- [ ] vm
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- [ ] worker_threads
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- [ ] zlib
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* [x] node globals _partly_
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### Deprecated
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These builtins are deprecated in NodeJS v13 and will probably not be polyfilled:
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- constants
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- domain
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- freelist
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- punycode
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### Experimental
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These builtins are experimental in NodeJS v13 and will not be polyfilled until
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they are stable:
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- async_hooks
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- inspector
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- policies
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- report
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- trace_events
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- wasi
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## CommonJS Module Loading
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`createRequire(...)` is provided to create a `require` function for loading CJS
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modules. It also sets supported globals.
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```ts
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import { createRequire } from "https://deno.land/std@$STD_VERSION/node/module.ts";
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const require = createRequire(import.meta.url);
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// Loads native module polyfill.
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const path = require("path");
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// Loads extensionless module.
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const cjsModule = require("./my_mod");
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// Visits node_modules.
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const leftPad = require("left-pad");
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```
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## Contributing
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When converting from promise-based to callback-based APIs, the most obvious way
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is like this:
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```ts
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promise.then((value) => callback(null, value)).catch(callback);
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```
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This has a subtle bug - if the callback throws an error, the catch statement
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will also catch _that_ error, and the callback will be called twice. The correct
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way to do it is like this:
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```ts
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promise.then((value) => callback(null, value), callback);
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```
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The second parameter of `then` can also be used to catch errors, but only errors
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from the existing promise, not the new one created by the callback.
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If the Deno equivalent is actually synchronous, there's a similar problem with
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try/catch statements:
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```ts
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try {
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const value = process();
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callback(null, value);
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} catch (err) {
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callback(err);
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}
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```
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Since the callback is called within the `try` block, any errors from it will be
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caught and call the callback again.
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The correct way to do it is like this:
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```ts
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let err, value;
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try {
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value = process();
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} catch (e) {
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err = e;
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}
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if (err) {
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callback(err); // Make sure arguments.length === 1
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} else {
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callback(null, value);
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}
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```
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It's not as clean, but prevents the callback being called twice.
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