for (var s, i = 1, n = arguments.length; i <n;i++){
s = arguments[i];
for (var p in s) if (Object.prototype.hasOwnProperty.call(s, p))
t[p] = s[p];
}
return t;
};
exports.x = {};
exports.y = __assign({}, exports.x);
```
will instead be emitted as something like the following:
```ts
var tslib_1 = require("tslib");
exports.x = {};
exports.y = tslib_1.__assign({}, exports.x);
```
Because this can avoid duplicate declarations of things like `__extends`, `__assign`, etc., this means delivering users smaller files on average, as well as less runtime overhead.
For optimized bundles with TypeScript, you should absolutely consider using `tslib` and `--importHelpers`.
# Installing
For the latest stable version, run:
## npm
```sh
# TypeScript 2.3.3 or later
npm install --save tslib
# TypeScript 2.3.2 or earlier
npm install --save tslib@1.6.1
```
## yarn
```sh
# TypeScript 2.3.3 or later
yarn add tslib
# TypeScript 2.3.2 or earlier
yarn add tslib@1.6.1
```
## bower
```sh
# TypeScript 2.3.3 or later
bower install tslib
# TypeScript 2.3.2 or earlier
bower install tslib@1.6.1
```
## JSPM
```sh
# TypeScript 2.3.3 or later
jspm install tslib
# TypeScript 2.3.2 or earlier
jspm install tslib@1.6.1
```
# Usage
Set the `importHelpers` compiler option on the command line:
```
tsc --importHelpers file.ts
```
or in your tsconfig.json:
```json
{
"compilerOptions": {
"importHelpers": true
}
}
```
#### For bower and JSPM users
You will need to add a `paths` mapping for `tslib`, e.g. For Bower users:
