[[client-usage]]
== Usage

Using the client is straightforward, it supports all the public APIs of {es}, 
and every method exposes the same signature.


[source,js]
----
const { Client } = require('@elastic/elasticsearch')
const client = new Client({ node: 'http://localhost:9200' })

// promise API
const result = await client.search({
  index: 'my-index',
  body: {
    query: {
      match: { hello: 'world' }
    }
  }
})

// callback API
client.search({
  index: 'my-index',
  body: {
    query: {
      match: { hello: 'world' }
    }
  }
}, (err, result) => {
  if (err) console.log(err)
})
----

The returned value of every API call is formed as follows:

[source,ts]
----
{
  body: object | boolean
  statusCode: number
  headers: object
  warnings: [string],
  meta: object
}
----

NOTE: The body is a boolean value when you use `HEAD` APIs.

The above value is returned even if there is an error during the execution of 
the request, this means that you can safely use the 
https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Operators/Destructuring_assignment[destructuring assignment].

The `meta` key contains all the information about the request, such as attempt, 
options, and the connection that has been used.

[source,js]
----
// promise API
const { body } = await client.search({
  index: 'my-index',
  body: {
    query: {
      match: { hello: 'world' }
    }
  }
})

// callback API
client.search({
  index: 'my-index',
  body: {
    query: {
      match: { hello: 'world' }
    }
  }
}, (err, { body }) => {
  if (err) console.log(err)
})
----


=== Aborting a request

If needed, you can abort a running request by calling the `request.abort()` method returned by the API.

CAUTION: If you abort a request, the request will fail with a `RequestAbortedError`.


[source,js]
----
const request = client.search({
  index: 'my-index',
  body: {
    query: {
      match: { hello: 'world' }
    }
  }
}, {
  ignore: [404],
  maxRetries: 3
}, (err, result) => {
  if (err) {
    console.log(err) // RequestAbortedError
  } else {
    console.log(result)
  }
})

request.abort()
----

The same behavior is valid for the promise style API as well.
[source,js]
----
const request = client.search({
  index: 'my-index',
  body: {
    query: {
      match: { hello: 'world' }
    }
  }
}, {
  ignore: [404],
  maxRetries: 3
})

request
  .then(result => console.log(result))
  .catch(err => console.log(err)) // RequestAbortedError

request.abort()
----


=== Request specific options
If needed you can pass request specific options in a second object:

[source,js]
----
// promise API
const result = await client.search({
  index: 'my-index',
  body: {
    query: {
      match: { hello: 'world' }
    }
  }
}, {
  ignore: [404],
  maxRetries: 3
})

// callback API
client.search({
  index: 'my-index',
  body: {
    query: {
      match: { hello: 'world' }
    }
  }
}, {
  ignore: [404],
  maxRetries: 3
}, (err, { body }) => {
  if (err) console.log(err)
})
----


The supported request specific options are:
[cols=2*]
|===
|`ignore`
|`[number]` -  HTTP status codes which should not be considered errors for this request. +
_Default:_ `null`

|`requestTimeout`
|`number` - Max request timeout for the request in milliseconds, it overrides the client default. +
_Default:_ `30000`

|`maxRetries`
|`number` - Max number of retries for the request, it overrides the client default. +
_Default:_ `3`

|`compression`
|`string, boolean` - Enables body compression for the request. +
_Options:_ `false`, `'gzip'` +
_Default:_ `false`

|`asStream`
|`boolean` - Instead of getting the parsed body back, you get the raw Node.js stream of data. +
_Default:_ `false`

|`headers`
|`object` - Custom headers for the request. +
_Default:_ `null`

|`querystring`
|`object` - Custom querystring for the request. +
_Default:_ `null`

|`id`
|`any` - Custom request id. _(overrides the top level request id generator)_ +
_Default:_ `null`

|`context`
|`any` - Custom object per request. _(you can use it to pass data to the clients events)_ +
_Default:_ `null`
|===


=== Error handling

The client exposes a variety of error objects that you can use to enhance your 
error handling. You can find all the error objects inside the `errors` key in 
the client.

[source,js]
----
const { errors } = require('@elastic/elasticsearch')
console.log(errors)
----


You can find the errors exported by the client in the table below.

[cols=3*]
|===
|*Error*
|*Description*
|*Properties*

|`ElasticsearchClientError`
|Every error inherits from this class, it is the basic error generated by the client.
a|* `name` - `string`
* `message` - `string`

|`TimeoutError`
|Generated when a request exceeds the `requestTimeout` option.
a|* `name` - `string`
* `message` - `string`
* `meta` - `object`, contains all the information about the request

|`ConnectionError`
|Generated when an error occurs during the request, it can be a connection error or a malformed stream of data.
a|* `name` - `string`
* `message` - `string`
* `meta` - `object`, contains all the information about the request

|`RequestAbortedError`
|Generated if the user calls the `request.abort()` method.
a|* `name` - `string`
* `message` - `string`
* `meta` - `object`, contains all the information about the request

|`NoLivingConnectionsError`
|Given the configuration, the ConnectionPool was not able to find a usable Connection for this request.
a|* `name` - `string`
* `message` - `string`
* `meta` - `object`, contains all the information about the request

|`SerializationError`
|Generated if the serialization fails.
a|* `name` - `string`
* `message` - `string`
* `data` - `object`, the object to serialize

|`DeserializationError`
|Generated if the deserialization fails.
a|* `name` - `string`
* `message` - `string`
* `data` - `string`, the string to deserialize

|`ConfigurationError`
|Generated if there is a malformed configuration or parameter.
a|* `name` - `string`
* `message` - `string`

|`ResponseError`
|Generated when in case of a `4xx` or `5xx` response.
a|* `name` - `string`
* `message` - `string`
* `meta` - `object`, contains all the information about the request
* `body` - `object`, the response body
* `statusCode` - `object`, the response headers
* `headers` - `object`, the response status code
|===