| write(string eventName, EventType type, object keyValues, AsyncCallback\<void> callback): void | void | Logs application events in asynchronous mode. This method uses an asynchronous callback to return the result. |
| write(string eventName, EventType type, object keyValues): Promise\<void> | Promise\<void> | Logs application events in asynchronous mode. This method uses a promise to return the result. |
-**eventName**: event name you customized. The event name can contain a maximum of 48 characters, including digits (0 to 9), letters (a to z), and underscores (\_). It must start with a letter.
-**type**: event type enumerated by **EventType**.
| Type | Description |
| --------- | ----------------- |
| FAULT | Fault event |
| STATISTIC | Statistical event |
| SECURITY | Security event |
| BEHAVIOR | Behavior event |
-**keyValues**: event parameter key-value pair. For a variable-length parameter, enter each pair of parameter name and value in sequence. For a JSON parameter, enter the parameter name as the key and parameter value as the value.
- A parameter name must be a string, and a parameter value must be a string, number, boolean, or array (which is a basic element).
- The number of event parameters must be less than or equal to 32.
- The parameter name can contain a maximum of 16 characters, including digits (0 to 9), letters (a to z), and underscores (\_). It must start with a letter and cannot end with an underscore (\_).
- A string value can contain a maximum of 8*1024 characters.
- An array value can contain a maximum of 100 elements. Excess elements will be truncated.
-**callback**: callback function used to process the received return value. The value **0** indicates that the event parameter verification is successful, and the event will be written to the event file asynchronously. A value greater than **0** indicates that invalid parameters are present in the event, and the event will be written to the event file asynchronously after the invalid parameters are ignored. A value smaller than **0** indicates that the event parameter verification fails, and the event will not be written to the event file asynchronously.
When an asynchronous callback is used, the return value can be processed directly in the callback. When a promise is used, the return value can also be processed in the promise in a similar way. For details about the result codes, see [Event Verification Result Codes](hiappevent-overview.md#Event Verification Result Codes).
| configure(ConfigOption config) | boolean | Sets the configuration options for application event logging.<br/>The value **true** indicates that the operation is successful, and value **false** indicates the opposite. |
-**config**: configuration options for application event logging.
Configuration options for application event logging (**ConfigOption**)
| disable | boolean | No | Sets the application event logging switch. The value **true** means to disable the application event logging function, and value **false** means the opposite. |
| maxStorage | string | No | Specifies the maximum size of the event file storage directory. The default value is 10M. |
| DISTRIBUTED_SERVICE_NAME | string | Distributed service name. |
| DISTRIBUTED_SERVICE_INSTANCE_ID | string | Distributed service instance ID. |
## How to Develop
In this example, an application event is logged after the application startup execution page is loaded.
1. Create a JS application project. In the displayed Project window, choose **entry > src > main** > **js** > **default** > **pages > index**, and double-click index.js. Add the code to log the initial application event after page loading. The sample code is as follows:
HiAppEvent provides event logging APIs for applications to log the fault, statistical, security, and user behavior events reported during running. Based on event information, you will be able to analyze the running status of your application.
## Basic Concepts
The HiAppEvent module of OpenHarmony can be used to develop application event services and provide functions related to application events, including flushing application events to a disk and querying historical application event data.
-**Logging**
Logs changes caused by user operations to provide service data for development, product, and O&M analysis.
## Event Verification Result Codes
| Result Code | Cause | Check Rule | Processing Method |
| 0 | None | Event verification is successful. | Event logging is normal. No action is required. |
| -1 | Invalid event name | The event name is not empty and contains a maximum of 48 characters.<br/>The event name consists of only the following characters: digits (0 to 9), letters (a to z), and underscore (\_).<br/>The event name does not start with a digit or underscore (_). | Ignore this event and do not perform logging. |
| -2 | Invalid event parameter type | The event name must be a string.<br/>The event type must be a number.<br/>The key value must be an object. | Ignore this event and do not perform logging. |
| -99 | Application event logging disabled | The application event logging function is disabled. | Ignore this event and do not perform logging. |
| -100 | Unknown error | None | Ignore this event and do not perform logging. |
| 1 | Invalid key name | The key name is not empty and contains a maximum of 16 characters.<br/>The key name consists of only the following characters: digits (0 to 9), letters (a to z), and underscore (\_).<br/>The key name does not start with a digit or underscore (\_).<br/>The key name does not end with an underscore (_). | Ignore the key-value pair and continue to perform logging. |
| 2 | Invalid key type | The key must be a string. | Ignore the key-value pair and continue to perform logging. |
| 3 | Invalid value type | The supported value types vary depending on the programming language:<br/>boolean, number, string, or Array [basic element] | Ignore the key-value pair and continue to perform logging. |
| 4 | Value too long | The value can contain a maximum of 8*1024 characters. | Ignore the key-value pair and continue to perform logging. |
| 5 | Excess key-value pairs | The number of key-value pairs must be less than or equal to 32. | Ignore the excess key-value pairs and continue to perform logging. |
| 6 | Excess elements in a list value | The number of elements in a list value must be less than or equal to 100. | Truncate the list with only the first 100 elements retained, and continue to perform logging. |
| 7 | Invalid list value | A list value can only be a basic element.<br/>The elements in a list value must be of the same type. | Ignore the key-value pair and continue to perform logging. |
