---
layout: api
id: promise.getnewlibrarycopy
title: Promise.getNewLibraryCopy
---
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<div class="api-code-section"><markdown>
##Promise.getNewLibraryCopy
```js
Promise.getNewLibraryCopy() -> Object
```
Returns a new independent copy of the Bluebird library.
This method should be used before you use any of the methods which would otherwise alter the global `Bluebird` object - to avoid polluting global state.
A basic example:
```js
var Promise = require('bluebird');
var Promise2 = Promise.getNewLibraryCopy();
Promise2.x = 123;
console.log(Promise2 == Promise); // false
console.log(Promise2.x); // 123
console.log(Promise.x); // undefined
```
`Promise2` is independent to `Promise`. Any changes to `Promise2` do not affect the copy of Bluebird returned by `require('bluebird')`.
In practice:
```js
var Promise = require('bluebird').getNewLibraryCopy();
Promise.coroutine.addYieldHandler( function() { /* */ } ); // alters behavior of `Promise.coroutine()`
// somewhere in another file or module in same app
var Promise = require('bluebird');
Promise.coroutine(function*() {
// this code is unaffected by the yieldHandler defined above
// because it was defined on an independent copy of Bluebird
});
```
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