JavaScript policy

This page applies to Apigee and Apigee hybrid.

View Apigee Edge documentation.

The JavaScript policy lets you add custom JavaScript code that executes in the context of the API proxy flow. This policy lets you implement custom behavior not otherwise covered by Apigee policies.

In your custom JavaScript code, you can use the objects, methods, and properties of the Apigee JavaScript object model. You can get, set, and remove variables in the proxy flow context, execute custom logic, perform fault handling, extract data from requests or responses, and dynamically edit the backend target URL. You can also use basic cryptographic functions that are available in the object model.

The JavaScript policy lets you specify a JavaScript source file to execute, or you can include JavaScript code directly in the policy's configuration using the <Source> element. Either way, the JavaScript code executes when the step where the policy is attached executes.

For the source file option, the source code is always stored in a standard location in the proxy bundle: apiproxy/resources/jsc. Or, you can store the source code in a resource file at the environment or organization level. For instructions, see Resource files. You can also upload JavaScript using the Apigee UI proxy editor.

Apigee does not recommend using the JavaScript policy for the following:

• Logging. The MessageLogging policy is better suited for logging with third-party logging platforms such as Splunk, Sumo, and Loggly. This policy also improves API proxy performance by executing in the PostClientFlow after the response returns to the client.
• Replacing Apigee policies. The JavaScript policy does not replace the capabilities of Apigee policies. If the capabilities you need are available in an Apigee policy, use that policy instead of implementing a custom JavaScript solution. Custom JavaScript code might not match the performance and optimization of Apigee policies.

JavaScript source files must have a .js extension.

Apigee supports JavaScript running on the Rhino JavaScript engine 1.7.13.

This policy is an Extensible policy and use of this policy might have cost or utilization implications, depending on your Apigee license. For information on policy types and usage implications, see Policy types.

Samples

Rewrite the target URL

A common use case involves extracting data from a request body, storing it in a flow variable, and then using that flow variable elsewhere in the proxy flow. For example, suppose a user enters their name in an HTML form and submits it. To extract the form data and dynamically add it to the backend service URL, use a JavaScript policy.

Note: To try this example, create a new proxy in the proxy editor. When you create the proxy, provide a backend service URL, for example, http://www.example.com. This example dynamically rewrites the backend URL. If you need to create a new proxy, see the getting started tutorial.

1. In the Apigee UI, open the proxy you created in the proxy editor.
2. Select the Develop tab.
3. From the New menu, select New Script.
4. In the dialog, select JavaScript and name the script js-example.
5. Paste the following code in the code editor and save the proxy. The context object is available to JavaScript code anywhere in the proxy flow. It obtains flow-specific constants, calls useful get/set methods, and performs other operations. This object is part of the Apigee JavaScript object model. The target.url flow variable is a built-in, read/write variable accessible in the Target Request flow. When you set that variable with the API URL, Apigee calls that backend URL. This rewrites the original target URL, which was the URL you specified when you created the proxy (for example, http://www.example.com).

   if (context.flow=="PROXY_REQ_FLOW") {
        var username = context.getVariable("request.formparam.user");
        context.setVariable("info.username", username);
   }
   
   
   if (context.flow=="TARGET_REQ_FLOW") {
        context.setVariable("request.verb", "GET");
        var name = context.getVariable("info.username");
        var url = "http://mocktarget.apigee.net/"
        context.setVariable("target.url", url + "?user=" + name);
   }

6. From the New Policy menu, select JavaScript.
7. Name the policy target-rewrite. Accept the defaults, and save the policy.
8. After you select the Proxy Endpoint Preflow in the Navigator, the policy is added to that flow.
9. In the Navigator, select Target Endpoint PreFlow.
10. In the Navigator, drag the JavaScript policy onto the Request side of the Target Endpoint in the flow editor.
11. Save.
12. Substitute your organization name and proxy name when you call the API:

curl -i -H 'Content-Type: application/x-www-form-urlencoded' -X POST -d 'user=Will' http://myorg-test.apigee.net/js-example

Examine the XML definition for the JavaScript policy used in this example. The <ResourceURL> element specifies the JavaScript source file to execute. This pattern applies to any JavaScript source file: jsc://filename.js. If your JavaScript code requires includes, use one or more <IncludeURL> elements, as described later in this document.

<?xml version="1.0" encoding="UTF-8" standalone="yes"?>
<Javascript async="false" continueOnError="false" enabled="true" timeLimit="200" name="target-rewrite">
    <DisplayName>target-rewrite</DisplayName>
    <Properties/>
    <ResourceURL>jsc://js-example.js</ResourceURL>
</Javascript>

Retrieve property value from JavaScript

You can add a <Property> element in the configuration and then retrieve its value with JavaScript at runtime.

Use the element's name attribute to specify the name for accessing the property from JavaScript code. The <Property> element's value (the value between the opening and closing tags) is the literal value JavaScript receives.

In JavaScript, you retrieve the policy property value by accessing it as a property of the Properties object, as follows:

• Configure the property. The property value is the variable name response.status.code.

  <Javascript async="false" continueOnError="false" enabled="true" timeLimit="200" name="JavascriptURLRewrite">
      <DisplayName>JavascriptURLRewrite</DisplayName>
      <Properties>
          <Property name="source">response.status.code</Property>
      </Properties>
      <ResourceURL>jsc://JavascriptURLRewrite.js</ResourceURL>
  </Javascript>

• Retrieve the property using JavaScript. The getVariable function then uses the retrieved variable name to retrieve the variable's value.

  var responseCode = properties.source; // Returns "response.status.code"
  var value = context.getVariable(responseCode); // Get the value of response.status.code
  context.setVariable("response.header.x-target-response-code", value);

Handling errors

For examples and a discussion of error handling techniques you can use in a JavaScript callout, see Correct way to return an error from a JavaScript policy. Suggestions in the Apigee Community are for informational purposes only and do not necessarily represent best practices recommended by Google.

Within a JavaScript policy, accessing request.content.asJSON in read-only mode converts large integers to exponential notation in the message body. This overwrites the message with the converted values.

Element reference

The element reference describes the elements and attributes of the JavaScript policy.

<?xml version="1.0" encoding="UTF-8" standalone="yes"?>
<Javascript async="false"
        continueOnError="false" enabled="true" timeLimit="200"
        name="JavaScript-1">
    <DisplayName>JavaScript 1</DisplayName>
    <Properties>
        <Property name="propName">propertyValue</Property>
    </Properties>
    <SSLInfo>
        <Enabled>trueFalse</Enabled>
        <ClientAuthEnabled>trueFalse</ClientAuthEnabled>
        <KeyStore>ref://keystoreRef</KeyStore>
        <KeyAlias>keyAlias</KeyAlias>
        <TrustStore>ref://truststoreRef</TrustStore>
    </SSLInfo>
    <IncludeURL>jsc://a-javascript-library-file</IncludeURL>
    <ResourceURL>jsc://my-javascript-source-file</ResourceURL>
    <Source>insert_js_code_here</Source>
</Javascript>

<Javascript> Attributes

< languageVersion="VERSION_1_3" Javascript name="Javascript-1" enabled="true" continueOnError="false" async="false" timeLimit="200">

Attribute	Description	Default	Presence
languageVersion	Specifies the version of the JavaScript language the code is written in. Values include VERSION_DEFAULT, VERSION_1_0, VERSION_1_1, VERSION_1_2, VERSION_1_3, VERSION_1_4, VERSION_1_5, VERSION_1_6, VERSION_1_7, VERSION_1_8, and VERSION_ES6.	VERSION_DEFAULT	Optional
timeLimit	Specifies the maximum time (in milliseconds) a script can execute. For example, if a 200 ms limit is exceeded, the policy throws this error: Javascript.policy_name failed with error: Javascript runtime exceeded limit of 200ms. Note: For free trial accounts, execution time is limited to 200 ms.	N/A	Required

The following table describes attributes that are common to all policy parent elements:

Attribute	Description	Default	Presence
name	The internal name of the policy. The value of the name attribute can contain letters, numbers, spaces, hyphens, underscores, and periods. This value cannot exceed 255 characters. Optionally, use the <DisplayName> element to label the policy in the management UI proxy editor with a different, natural-language name.	N/A	Required
continueOnError	Set to false to return an error when a policy fails. This is expected behavior for most policies. Set to true to have flow execution continue even after a policy fails. See also: Fault rules are triggered ONLY in an error state (about continueOnError) Handling faults within the current flow	false	Optional
enabled	Set to true to enforce the policy. Set to false to turn off the policy. The policy will not be enforced even if it remains attached to a flow.	true	Optional
async	This attribute is deprecated.	false	Deprecated

<DisplayName> element

Use in addition to the name attribute to label the policy in the management UI proxy editor with a different, natural-language name.

<DisplayName>Policy Display Name</DisplayName>

Default	N/A If you omit this element, the value of the policy's name attribute is used.
Presence	Optional
Type	String

<IncludeURL> element

Specifies a JavaScript library file to load as a dependency for the main JavaScript file specified with the <ResourceURL> or <Source> element. The policy evaluates the scripts in the order in which they are listed in the policy. Your code can use the objects, methods, and properties of the JavaScript object model.

Include more than one JavaScript dependency resource using additional <IncludeURL> elements.

Warning: If your JavaScript files are stored at the proxy or environment level, ensure you upload them correctly with cURL using the -F option or as a file attachment through a REST client. The Content-Type is multipart/form-data. For more information, see Managing resources.

<IncludeURL>jsc://my-javascript-dependency.js</IncludeURL>

Default:	None
Presence:	Optional
Type:	String

<Property> element

Specifies a property you can access from JavaScript code at runtime.

<Properties>
    <Property name="propName">propertyValue</Property>
</Properties>

Default:	None
Presence:	Optional
Type:	String

Attributes

Attribute	Description	Default	Presence
name	Specifies the name of the property.	N/A	Required

Example

See the example in the Samples section.

<ResourceURL> element

Specifies the main JavaScript file that executes in the API flow. You can store this file at the API proxy scope (under /apiproxy/resources/jsc in the API proxy bundle or in the Scripts section of the API proxy editor's Navigator pane). Alternatively, store it at the organization or environment scopes for reuse across multiple API proxies, as described in Managing resources. Your code can use the objects, methods, and properties of the JavaScript object model.

<ResourceURL>jsc://my-javascript.js</ResourceURL>

Default:	None
Presence:	Either <ResourceURL> or <Source> is required. If both <ResourceURL> and <Source> are present, the policy ignores <ResourceURL>.
Type:	String

Example

See the example in the Samples section.

<Source> element

You can insert JavaScript directly into the policy's XML configuration. The inserted JavaScript code executes when the policy executes in the API flow.

Default:	None
Presence:	Either <ResourceURL> or <Source> is required. If both <ResourceURL> and <Source> are present, the policy ignores <ResourceURL>.
Type:	String

Example

<Javascript name='JS-ParseJsonHeaderFullString' timeLimit='200' >
  <Properties>
    <Property name='inboundHeaderName'>specialheader</Property>
    <Property name='outboundVariableName'>json_stringified</Property>
  </Properties>
  <Source>
var varname = 'request.header.' + properties.inboundHeaderName + '.values.string';
var h = context.getVariable(varname);
if (h) {
  h = JSON.parse(h);
  h.augmented = (new Date()).valueOf();
  var v = JSON.stringify(h, null, 2) + '\n';
  // further indent
  var r = new RegExp('^(\S*)','mg');
  v= v.replace(r,'    $1');
  context.setVariable(properties.outboundVariableName, v);
}
  </Source>
</Javascript>

<SSLInfo> element

Specifies the properties used to configure TLS for all HTTP client instances created by the JavaScript policy.

    <SSLInfo>
        <Enabled>trueFalse</Enabled>
        <ClientAuthEnabled>trueFalse</ClientAuthEnabled>
        <KeyStore>ref://keystoreRef</KeyStore>
        <KeyAlias>keyAlias</KeyAlias>
        <TrustStore>ref://truststoreRef</TrustStore>
    </SSLInfo>

Default:	None
Presence:	Optional
Type:	String

The process of configuring TLS for an HTTP client is the same process used to configure TLS for a TargetEndpoint/TargetServer. See Options for configuring TLS for more information.

Usage notes

Warning: The security model does not permit system calls. For example, internal file system reads or writes, current user information, process lists, or CPU/memory utilization are not permitted. Although some calls might be functional, they are unsupported and subject to active disablement at any time. For forward compatibility, avoid making these calls in your code.

Debugging JavaScript policy code

Use the print() function to output debug information to the transaction output panel in the Debug tool. For details and examples, see Debug JavaScript with print() statements.

To view print statements in the Debug tool:

1. Open the Debug tool and start a trace session for a proxy that contains your JavaScript policy.
2. Call the proxy.
3. In the Debug Tool, click Output from all Transactions to open the output panel.

   

4. Your print statements appear in this panel.

Flow Variables

This policy does not populate any variables by default. However, you can set and get flow variables in your JavaScript code by calling methods on the context object. For example:

context.setVariable("response.header.X-Apigee-Target", context.getVariable("target.name"))

The context object is part of the Apigee JavaScript object model.

Error reference

This section describes the fault codes and error messages that are returned and fault variables that are set by Apigee when this policy triggers an error. This information is important to know if you are developing fault rules to handle faults. To learn more, see What you need to know about policy errors and Handling faults.

Runtime errors

These errors can occur when the policy executes.

Tip: Need help resolving an error? Click in the Fix column for detailed troubleshooting information.

Fault code	HTTP status	Cause	Fix
steps.javascript.ScriptExecutionFailed	500	The JavaScript policy can throw many different types of ScriptExecutionFailed errors. Commonly seen types of errors include RangeError, ReferenceError, SyntaxError, TypeError, and URIError.
steps.javascript.ScriptExecutionFailedLineNumber	500	An error occurred in the JavaScript code. See the fault string for details.	N/A
steps.javascript.ScriptSecurityError	500	A security error occurred when the JavaScript executed. See the fault string for details.	N/A

Deployment errors

These errors can occur when you deploy a proxy containing this policy.

Tip: Need help resolving an error? Click next to the error's cause description to visit the troubleshooting page.

Error name	Cause	Fix
InvalidResourceUrlFormat	If the format of the resource URL specified within the <ResourceURL> or the <IncludeURL> element of the JavaScript policy is invalid, then the deployment of the API proxy fails.
InvalidResourceUrlReference	If the <ResourceURL> or the <IncludeURL> elements refer to a JavaScript file that does not exist, then the deployment of the API proxy fails. The referenced source file must exist either the API proxy, environment, or organization level.
WrongResourceType	This error occurs during deployment if the <ResourceURL> or the <IncludeURL> elements of the JavaScript policy refer to any resource type other than jsc (JavaScript file).
NoResourceURLOrSource	The deployment of the JavaScript policy can fail with this error if the <ResourceURL> element is not declared or if the resource URL is not defined within this element. <ResourceURL> element is a mandatory element. Or, The <IncludeURL> element is declared but the resource URL is not defined within this element. The <IncludeURL> element is optional but if declared, the resource URL must be specified within the <IncludeURL> element.

Fault variables

These variables are set when this policy triggers an error at runtime. For more information, see What you need to know about policy errors.

Variables	Where	Example
fault.name="fault_name"	fault_name is the name of the fault, as listed in the Runtime errors table above. The fault name is the last part of the fault code.	fault.name Matches "ScriptExecutionFailed"
javascript.policy_name.failed	policy_name is the user-specified name of the policy that threw the fault.	javascript.JavaScript-1.failed = true

Example error response

Note: For error handling, the best practice is to trap the errorcode part of the error response. Do not rely on the text in the faultstring, because it could change.

{
  "fault": {
    "faultstring": "Execution of SetResponse failed with error: Javascript runtime error: "ReferenceError: "status" is not defined. (setresponse.js:6)\"",
    "detail": {
      "errorcode": "steps.javascript.ScriptExecutionFailed"
    }
  }
}

Example fault rule

<FaultRule name="JavaScript Policy Faults">
    <Step>
        <Name>AM-CustomErrorResponse</Name>
        <Condition>(fault.name Matches "ScriptExecutionFailed") </Condition>
    </Step>
    <Condition>(javascript.JavaScript-1.failed = true) </Condition>
</FaultRule>

Schema

Each policy type is defined by an XML schema (.xsd). For reference, policy schemas are available on GitHub.

Related topics

• JavaScript object model

Apigee Community articles

You can find these related articles in the Apigee Community:

• How to handle multi-value headers in JavaScript