Install it and write into package.json dependences.
```sh
$ npm install @alicloud/pop-core -S
```
## Prerequisite
Node.js >= 8.x
### Notes
You must know your `AK`(`accessKeyId/accessKeySecret`), and the cloud product's `endpoint` and `apiVersion`.
For example, The ECS OpenAPI(https://help.aliyun.com/document_detail/25490.html), the API version is `2014-05-26`.
And the endpoint list can be found at [here](https://help.aliyun.com/document_detail/25489.html), the center endpoint is ecs.aliyuncs.com. Add http protocol `http` or `https`, should be `http://ecs.aliyuncs.com/`.
## Online Demo
**[API Explorer](https://api.aliyun.com)** provides the ability to call the cloud product OpenAPI online, and dynamically generate SDK Example code and quick retrieval interface, which can significantly reduce the difficulty of using the cloud API. **It is highly recommended**.
One way is passing opts through the Client constructor. You should treat opts passed through the constructor as default custom opts, because all requests will use this opts.
```js
var client = new RPCClient({
accessKeyId: '<accessKeyId>',
accessKeySecret: '<accessKeySecret>',
endpoint: '<endpoint>',
apiVersion: '<apiVersion>',
opts: {
timeout: 3000
}
});
```
Another way is passing opts through the function's parameter. You should use this way when you want to just pass opts in specific functions.
```js
client.request(action, params, {
timeout: 3000
});
```
When both ways are used, opts will be merged. But for the opt with the same key, the opts provided by the function parameter overrides the opts provided by the constructor.
### Http Proxy Support
```js
var tunnel = require('tunnel-agent');
var RPCClient = require('@alicloud/pop-core').RPCClient;