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/* This Source Code Form is subject to the terms of the Mozilla Public
* License, v. 2.0. If a copy of the MPL was not distributed with this
* file, You can obtain one at http://mozilla.org/MPL/2.0/. */
"use strict";
module.metadata = {
"stability": "unstable"
};
/**
* Merges all the properties of all arguments into first argument. If two or
* more argument objects have own properties with the same name, the property
* is overridden, with precedence from right to left, implying, that properties
* of the object on the left are overridden by a same named property of the
* object on the right.
*
* Any argument given with "falsy" value - commonly `null` and `undefined` in
* case of objects - are skipped.
*
* @examples
* var a = { bar: 0, a: 'a' }
* var b = merge(a, { foo: 'foo', bar: 1 }, { foo: 'bar', name: 'b' });
* b === a // true
* b.a // 'a'
* b.foo // 'bar'
* b.bar // 1
* b.name // 'b'
*/
function merge(source) {
let descriptor = {};
// `Boolean` converts the first parameter to a boolean value. Any object is
// converted to `true` where `null` and `undefined` becames `false`. Therefore
// the `filter` method will keep only objects that are defined and not null.
Array.slice(arguments, 1).filter(Boolean).forEach(function onEach(properties) {
Object.getOwnPropertyNames(properties).forEach(function(name) {
descriptor[name] = Object.getOwnPropertyDescriptor(properties, name);
});
});
return Object.defineProperties(source, descriptor);
}
exports.merge = merge;
/**
* Returns an object that inherits from the first argument and contains all the
* properties from all following arguments.
* `extend(source1, source2, source3)` is equivalent of
* `merge(Object.create(source1), source2, source3)`.
*/
function extend(source) {
let rest = Array.slice(arguments, 1);
rest.unshift(Object.create(source));
return merge.apply(null, rest);
}
exports.extend = extend;
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