1.0.0

README.md

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+# promise-while-loop
+
+An asynchronous while-loop implementation with full support for Promises - both for the main logic, and for the predicate function.
+
+## A word of caution
+
+Think __very carefully__ before using a while loop for asynchronous code. In many cases, it will be cleaner to simply *use recursion* - if the code is asynchronous, this will never cause stack overflows, no matter how many levels you nest. In fact, recursion is what this module uses internally; it's the only real way to implement asynchronous loops.
+
+A simple example of using recursion, __*without `promise-while-loop`*__:
+
+```javascript
+var Promise = require("bluebird");
+var bhttp = require("bhttp");
+
+function loop(pageNumber) {
+	return Promise.try(function() {
+		return bhttp.get("http://api.example.com/page/" + pageNumber);
+	}).then(function(response) {
+		if (response.headers["x-next-page"] != null) {
+			return Promise.try(function() {
+				return loop(response.headers["x-next-page"]);
+			}).then(function(recursiveResults) {
+				return [response.body].concat(recursiveResults);
+			});
+		}
+	});
+}
+
+Promise.try(function() {
+	var i = 0;
+	
+	return loop(1);
+}).then(function(results) {
+	// Now `results` is an array that contains the response for each HTTP request made.
+})
+```
+
+If you're sure that you can write cleaner code with a while loop than through recursion, then this is the module for you :)
+
+## License
+
+[WTFPL](http://www.wtfpl.net/txt/copying/) or [CC0](https://creativecommons.org/publicdomain/zero/1.0/), whichever you prefer. A donation and/or attribution are appreciated, but not required.
+
+## Donate
+
+My income consists largely of donations for my projects. If this module is useful to you, consider [making a donation](http://cryto.net/~joepie91/donate.html)!
+
+You can donate using Bitcoin, PayPal, Flattr, cash-in-mail, SEPA transfers, and pretty much anything else.
+
+## Contributing
+
+Pull requests welcome. Please make sure your modifications are in line with the overall code style, and ensure that you're editing the files in `src/`, not those in `lib/`.
+
+Build tool of choice is `gulp`; simply run `gulp` while developing, and it will watch for changes.
+
+Be aware that by making a pull request, you agree to release your modifications under the licenses stated above.
+
+## Usage
+
+A simple (contrived) example:
+
+```javascript
+var i = 0;
+
+Promise.try(function() {
+	return whileLoop(function(lastResult) {
+		return Promise.try(function() {
+			return lastResult < 20;
+		}).delay(500); // Artificial delay, to prove that this really is asynchronous
+	}, function(lastResult) {
+		return Promise.try(function() {
+			var currentIteration = i;
+			i += 1;
+			
+			console.log("Last iteration: " + lastResult + " // Current iteration: " + currentIteration + " // Next iteration: " + i);
+			
+			return currentIteration;			
+		});
+	});
+}).then(function(results) {
+	console.log("i: " + i + " // Results: " + results)
+});
+
+```
+
+## API
+
+### whileLoop(predicate, func)
+
+Initiates the loop. The loop will always run at least once - the `predicate` function will only be called *after* the first iteration.
+
+* __predicate__: This should be a function, returning either `true` or `false` (or a Promise that resolves to either of those) - depending on whether the loop should continue running or not. It receives a single argument, containing the result (return/resolve value) of the 'main function' from the last iteration.
+* __func__: This should be a function, optionally returning a Promise or synchronous value. It's the 'main' function that contains the 'body' of the loop - ie. the code that is executed on each iteration. It also receives a single argument, with the result of the last operation - except for the first iteration, where it contains `undefined`, as there is no previous result to provide.
+
+The `whileLoop` call will return a Promise, __collect the results__ into an (ordered) array, and resolve with that array once the loop has finished. Any kind of rejection/thrown error, in either the `predicate` function or the main body, will immediately abort the loop, and reject the returned Promise with the error that caused it.

gulpfile.js

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+var gulp = require('gulp');
+
+var gutil = require('gulp-util');
+var babel = require('gulp-babel');
+var cache = require('gulp-cached');
+var remember = require('gulp-remember');
+var plumber = require('gulp-plumber');
+
+var source = ["src/**/*.js"]
+
+gulp.task('babel', function() {
+	return gulp.src(source)
+		.pipe(plumber())
+		.pipe(cache("babel"))
+		.pipe(babel({presets: ["es2015"]}).on('error', gutil.log)).on('data', gutil.log)
+		.pipe(remember("babel"))
+		.pipe(gulp.dest("lib/"));
+});
+
+gulp.task('watch', function () {
+	gulp.watch(source, ['babel']);
+});
+
+gulp.task('default', ['babel', 'watch']);

index.js

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+'use strict';
+
+module.exports = require("./lib");

lib/index.js

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+'use strict';
+
+var Promise = require("bluebird");
+
+module.exports = function promiseWhile(predicate, func) {
+	var results = [];
+
+	function iteration(value) {
+		return Promise.try(function () {
+			return func(value);
+		}).then(function (result) {
+			results.push(result);
+
+			return Promise.try(function () {
+				return predicate(result);
+			}).then(function (predicateResult) {
+				if (predicateResult) {
+					return iteration(result);
+				} else {
+					return results;
+				}
+			});
+		});
+	}
+
+	return iteration();
+};

package.json

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+{
+  "name": "promise-while-loop",
+  "version": "1.0.0",
+  "description": "An asynchronous while-loop implementation with full support for Promises",
+  "main": "index.js",
+  "scripts": {
+    "test": "echo \"Error: no test specified\" && exit 1"
+  },
+  "repository": {
+    "type": "git",
+    "url": "git://github.com/joepie91/node-promise-while-loop"
+  },
+  "keywords": [
+    "while",
+    "promises",
+    "bluebird",
+    "recursion",
+    "loop"
+  ],
+  "author": "Sven Slootweg",
+  "license": "WTFPL",
+  "dependencies": {
+    "bluebird": "^3.3.3"
+  },
+  "devDependencies": {
+    "babel-preset-es2015": "^6.6.0",
+    "gulp": "^3.9.1",
+    "gulp-babel": "^6.1.2",
+    "gulp-cached": "^1.1.0",
+    "gulp-plumber": "^1.1.0",
+    "gulp-remember": "^0.3.0",
+    "gulp-util": "^3.0.7"
+  }
+}

src/index.js

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+'use strict';
+
+const Promise = require("bluebird");
+
+module.exports = function promiseWhile(predicate, func) {
+	let results = [];
+
+	function iteration(value) {
+		return Promise.try(() => {
+			return func(value);
+		}).then((result) => {
+			results.push(result);
+
+			return Promise.try(() => {
+				return predicate(result);
+			}).then((predicateResult) => {
+				if (predicateResult) {
+					return iteration(result);
+				} else {
+					return results;
+				}
+			});
+		});
+	}
+
+	return iteration();
+}

test.js

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+'use strict';
+
+const Promise = require("bluebird");
+const whileLoop = require("./");
+
+let i = 0;
+
+Promise.try(() => {
+	return whileLoop((lastResult) => {
+		return Promise.try(() => {
+			return lastResult < 20;
+		}).delay(500);
+	}, (lastResult) => {
+		return Promise.try(() => {
+			let currentIteration = i;
+			i += 1;
+			
+			console.log(`Last iteration: ${lastResult} // Current iteration: ${currentIteration} // Next iteration: ${i}`);
+			
+			return currentIteration;			
+		});
+	});
+}).then((results) => {
+	console.log(`i: ${i} // Results: ${results}`)
+})