Initial commit

.gitignore

+dist/
+
+# Dependency directories
+node_modules/
+
+# Logs
+logs/
+*.log
+npm-debug.log*
+
+# Optional npm cache directory
+.npm/
+
+# Optional REPL history
+.node_repl_history/

.gitlab-ci.yml

+stages:
+  - test
+
+before_script:
+  - yarn versions
+
+test:
+  stage: test
+  script:
+    - yarn
+    - yarn run test
+  tags:
+    - npm
+  artifacts:
+    paths:
+      - dist/

.npmignore

+.*
+src
+test
+gulpfile.js
+yarn.lock

README.md

+# Promised value
+A wrapper for values got asynchronously
+
+## Usage
+
+```js
+const data = new PromisedValue('Getting data...');
+console.log(data.value); // 'Getting data...'
+console.log(data.isReady); // false
+data.willBeReady.then(data => {
+	console.log(data); // 'Some data'
+});
+
+// ...
+
+data.value = 'Some data';
+console.log(data.value); // 'Some data'
+console.log(data.isReady); // true
+data.willBeReady.then(data => {
+	console.log(data); // 'Some data'
+});
+```

gulpfile.js

+const gulp      = require('gulp');
+const babel     = require('gulp-babel');
+const uglify    = require('gulp-uglify');
+
+const paths = new function() {
+	this.srcDir  = 'src';
+	this.distDir = 'dist';
+	
+	this.js    = this.srcDir + '/index.js';
+	this.jsOut = this.distDir;
+};
+
+// Scripts
+
+gulp.task('js', function () {
+	return gulp.src(paths.js)
+		.pipe(babel({
+			presets: ['env']
+		}))
+		.pipe(uglify({
+			compress: true,
+			mangle: {
+				toplevel: true
+			}
+		}))
+		.pipe(gulp.dest(paths.jsOut));
+});
+
+// Stages
+
+gulp.task('watch', function () {
+	gulp.watch(paths.js, gulp.task('js'));
+});
+
+gulp.task('build', gulp.task('js'));
+
+gulp.task('default', gulp.task('build'));

package.json

+{
+	"name":        "@gviagroup/promised-value",
+	"version":     "1.0.0",
+	"description": "A wrapper for values got asynchronously",
+	
+	"main": "dist/index.js",
+	
+	"scripts": {
+		"start": "gulp && concurrently \"gulp watch\" \"ava --fail-fast -w test\"",
+		"test":  "gulp && ava --verbose test"
+	},
+	
+	"devDependencies": {
+		"ava":              "^0.25.0",
+		"babel-core":       "^6.26.3",
+		"babel-preset-env": "^1.7.0",
+		"concurrently":     "^3.6.0",
+		"gulp":             "^4.0.0",
+		"gulp-babel":       "^7.0.1",
+		"gulp-uglify":      "^3.0.1"
+	}
+}

src/index.js

+'use strict';
+
+module.exports = PromisedValue;
+
+function PromisedValue(initialValue) {
+	if (!(this instanceof PromisedValue)) {
+		throw new TypeError("Cannot call a class as a function");
+	}
+	
+	let initialized    = false;
+	let value          = initialValue;
+	
+	let resolvePromise;
+	let willBeReady = new Promise(resolve => {
+		resolvePromise = resolve;
+	});
+	
+	Object.defineProperties(this, {
+		isReady: {
+			get() {
+				return initialized;
+			}
+		},
+		value: {
+			get() {
+				return value;
+			},
+			set(newValue) {
+				value = newValue;
+				
+				if (!initialized) {
+					resolvePromise(value);
+					initialized = true;
+				} else {
+					willBeReady = Promise.resolve(value);
+				}
+			}
+		},
+		willBeReady: {
+			get() {
+				return willBeReady;
+			}
+		}
+	});
+}

test/test.js

+const test = require('ava');
+
+const PV = require('../dist/index');
+
+test.cb('Promised value', t => {
+	t.plan(6);
+	
+	const v = new PV(42);
+	v.willBeReady.then(value => {
+		t.is(value, 123);
+	});
+	
+	t.is(v.isReady, false);
+	t.is(v.value, 42);
+	
+	v.value = 123;
+	
+	t.is(v.isReady, true);
+	t.is(v.value, 123);
+	
+	v.willBeReady.then(value => {
+		t.is(value, 123);
+		t.end();
+	});
+});
+
+test('Use new only', t => {
+	try {
+		PV();
+		t.fail('An exception should be thrown');
+	} catch (e) {
+		t.pass();
+	}
+});