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137 lines
3.9 KiB
137 lines
3.9 KiB
degenerator
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===========
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### Compiles sync functions into async functions
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[](https://github.com/TooTallNate/node-degenerator/actions?workflow=Node+CI)
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Sometimes you need to write sync looking code that's really async under the hood.
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This module takes a String to one or more synchronous JavaScript functions, and
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returns a new String that with those JS functions transpiled into `async`
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functions.
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So this:
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```js
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function foo() {
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return a('bar') || b();
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}
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```
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Gets compiled into:
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```js
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async function foo() {
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return await a('bar') || await b();
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}
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```
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With the compiled output code, you can evaluate the code using the `vm` module
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in Node.js, or save the code to a file and require it, or whatever.
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Installation
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------------
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Install with `npm`:
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```bash
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$ npm install degenerator
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```
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Example
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-------
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You must explicitly specify the names of the functions that should be
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"asyncified". So say we wanted to expose a `get(url)` function that did
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and HTTP request and returned the response body.
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The user has provided us with this implementation:
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``` js
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function myFn() {
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const one = get('https://google.com');
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const two = get('http://nodejs.org');
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const three = JSON.parse(get('http://jsonip.org'));
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return [one, two, three];
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}
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```
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Now we can compile this into an asyncronous function, implement the
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async `get()` function, and finally evaluate it into a real JavaScript function
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instance with the `vm` module:
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```typescript
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import vm from 'vm';
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import degenerator from 'degenerator';
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// The `get()` function is Promise-based (error handling omitted for brevity)
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function get(endpoint: string) {
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return new Promise((resolve, reject) => {
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var mod = 0 == endpoint.indexOf('https:') ? require('https') : require('http');
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var req = mod.get(endpoint);
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req.on('response', function (res) {
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var data = '';
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res.setEncoding('utf8');
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res.on('data', function (b) { data += b; });
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res.on('end', function () {
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resolve(data);
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});
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});
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});
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}
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// Convert the JavaScript string provided from the user (assumed to be `str` var)
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str = degenerator(str, [ 'get' ]);
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// Turn the JS String into a real async function instance
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const asyncFn = vm.runInNewContext(`(${str})`, { get });
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// Now we can invoke the function asynchronously
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asyncFn().then((res) => {
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// Do something with `res`...
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});
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```
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API
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---
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### degenerator(code: string, names: Array<string|RegExp>, options?: DegeneratorOptions): String
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Returns a "degeneratorified" JavaScript string, with `async`/`await` transplanted.
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#### DegeneratorOptions
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An options object _may_ be passed in as the third parameter, with the following
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values:
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* `output` - string - May be `"async"` or `"generator"`, defaults to `"async"`.
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License
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-------
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(The MIT License)
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Copyright (c) 2013 Nathan Rajlich <nathan@tootallnate.net>
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Permission is hereby granted, free of charge, to any person obtaining
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a copy of this software and associated documentation files (the
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'Software'), to deal in the Software without restriction, including
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without limitation the rights to use, copy, modify, merge, publish,
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distribute, sublicense, and/or sell copies of the Software, and to
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permit persons to whom the Software is furnished to do so, subject to
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the following conditions:
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The above copyright notice and this permission notice shall be
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included in all copies or substantial portions of the Software.
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THE SOFTWARE IS PROVIDED 'AS IS', WITHOUT WARRANTY OF ANY KIND,
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EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
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MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT.
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IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY
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CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT,
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TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE
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SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
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