Developing an Event Function

Function Syntax

You are advised to use Node.js 12.13.

Node.js 6.10
Use the following syntax when creating a handler function in Node.js 6.10:

export.handler = function(event, context, callback)
- handler: name of the function that FunctionGraph invokes to execute your code. The name must be consistent with that you define when creating a function.
- event: event parameter defined for the function. The parameter is in JSON format.
- context: runtime information provided for executing the function. For details, see SDK APIs.
- callback: used to return the defined err and message information to the frontend. The general syntax is callback(err, message). You can define the error or message content, for example, a character string.
- Function handler: index.handler.
  The function handler is in the format of [File name].[Function name]. For example, if you set the handler to index.handler in your function, FunctionGraph will load the handler function defined in the index.js file.
Node.js 8.10, Node.js 10.16, Node.js 12.13, and Node.js 14.18
Node.js 8.10, Node.js 10.16, Node.js 12.13, and Node.js 14.18 are compatible with the APIs of Node.js 6.10, and supports an async handler.

exports.handler = async (event, context, callback [optional]) => { return data;}

Responses are output through return.

Node.js Initializer

FunctionGraph supports the following Node.js runtimes:

Node.js6.10 (runtime = Node.js6)
Node.js8.10 (runtime = Node.js8)
Nodejs10.16(runtime = Node.js10)
Nodejs12.13(runtime = Node.js12)
Node.js14.18(runtime = Node.js14)
Node.js16.17(runtime = Node.js16)
Node.js18.15(runtime = Node.js18)

Initializer syntax:

[File name].[Initializer name]

For example, if the initializer is named index.initializer, FunctionGraph loads the initializer function defined in the index.js file.

To use Node.js to build initialization logic, define a Node.js function as the initializer. The following is a simple initializer:

exports.initializer = function(context, callback) {
    callback(null, '');
    };

Function Name
The function name exports.initializer must be the initializer function name specified for a function.

For example, if the initializer is named index.initializer, FunctionGraph loads the initializer function defined in the index.js file.
context
The context parameter contains the runtime information about a function. For example, request ID, temporary AK, and function metadata.
callback
The callback parameter is used to return the invocation result. The signature of this parameter is function(err, data), which is the same as that of the common callback parameter used in Node.js. If the value of err is not null, the function will return HandledInitializationError. The value of data is invalid because no value will be returned for function initialization. You can set the data parameter to null by referring to the previous example.

SDK APIs

Table 1 describes the context methods provided by FunctionGraph.

**Table 1** Context methods
Method	Description
getRequestID()	Obtains a request ID.
getRemainingTimeInMilliSeconds ()	Obtains the remaining running time of a function.
getAccessKey()	Obtains the AK (valid for 24 hours) with an agency. If you use this method, you need to configure an agency for the function. NOTE: FunctionGraph has stopped maintaining the getAccessKey API in the Runtime SDK. You cannot use this API to obtain a temporary AK.
getSecretKey()	Obtains the SK (valid for 24 hours) with an agency. If you use this method, you need to configure an agency for the function. NOTE: FunctionGraph has stopped maintaining the getSecretKey API in the Runtime SDK. You cannot use this API to obtain a temporary SK.
getSecurityAccessKey()	Obtains the SecurityAccessKey (valid for 24 hours) with an agency. If you use this method, you need to configure an agency for the function.
getSecuritySecretKey()	Obtains the SecuritySecretKey (valid for 24 hours) with an agency. If you use this method, you need to configure an agency for the function.
getSecurityToken()	Obtains the SecurityToken (valid for 24 hours) with an agency. If you use this method, you need to configure an agency for the function.
getUserData(string key)	Uses keys to obtain the values passed by environment variables.
getFunctionName()	Obtains the name of a function.
getRunningTimeInSeconds ()	Obtains the timeout of a function.
getVersion()	Obtains the version of a function.
getMemorySize()	Obtains the allocated memory.
getCPUNumber()	CPU usage of a function.
getPackage()	Obtains a function group, that is, an app.
getToken()	Obtains the token (valid for 24 hours) with an agency. If you use this method, you need to configure an agency for the function.
getLogger()	Obtains the logger method provided by the context and returns a log output class. Logs are output in the format of Time-Request ID-Content by using the info method. For example, use the info method to output logs: logg = context.getLogger() logg.info("hello")
getAlias	Obtains function alias.

Results returned by using the getToken(), getAccessKey(), and getSecretKey() methods contain sensitive information. Exercise caution when using these methods.

Execution Result

The execution result consists of the function output, summary, and log output.

**Table 2** Description of the execution result
Parameter	Successful Execution	Failed Execution
Function Output	The defined function output information is returned.	A JSON file that contains errorMessage and errorType is returned. The format is as follows: { "errorMessage": "", "errorType":"", } errorMessage: Error message returned by the runtime. errorType: Error type.
Summary	Request ID, Memory Configured, Execution Duration, Memory Used, and Billed Duration are displayed.	Request ID, Memory Configured, Execution Duration, Memory Used, and Billed Duration are displayed.
Log Output	Function logs are printed. A maximum of 4 KB logs can be displayed.	Error information is printed. A maximum of 4 KB logs can be displayed.