JavaScript policy

What

This policy lets you add custom JavaScript code that executes within the context of an API proxy flow. In your custom JavaScript code, you can use the objects, methods, and properties of the Apigee Edge JavaScript object model. The object model lets you get, set, and remove variables in the proxy flow context. You can also use basic cryptographic functions that are provided with the object model.

About

There are many use cases for the JavaScript policy. For example, you can get and set flow variables, execute custom logic and perform fault handling, extract data from requests or responses, dynamically edit the backend target URL, and much more. This policy allows you to implement custom behavior that is not covered by any other standard Edge policies. In fact, you can use a JavaScript policy to achieve many of the same behaviors implemented by other policies, like AssignMessage and ExtractVariable.

One use case we don't recommend for the JavaScript policy is logging. The Message Logging policy is much better suited for logging to third-party logging platforms such as Splunk, Sumo, and Loggly, and you improve API proxy performance by executing the Message Logging policy in the PostClientFlow, which executes after the response has been sent back to the client.

Basically, the JavaScript policy specifies the name of the JavaScript source file to execute when the step to which the policy is attached executes. The source file is always stored in a standard location within the proxy bundle: apiproxy/resources/jsc. Or, you can also store the source code in a resource file at the environment or organization level. For instructions, see Resource files. You can also upload your JavaScript through the management UI proxy editor.

JavaScript source files must always have a .js extension.

See Supported software and supported versions for the currently supported version of JavaScript.

Video

Watch a short video to learn how to create a custom policy extension using the JavaScript policy.

Samples

Rewrite the target URL

Here's a common use case: extracting data from a request body, storing it in a flow variable, and using that flow variable elsewhere in the proxy flow. Let's say you have an app where the user enters their name in an HTML form and submits it. You want the API proxy to extract the form data and dynamically add it to the URL used to call the backend service. How would you do this in a JavsScript policy?

Note: If you want to try out this example, we assume you've created a new proxy in the proxy editor. When you create it, just give it a backend service URL of: http://www.example.com. For this example, we're going to rewrite the backend URL dynamically. If you don't know how to create a new proxy, refer to the getting started tutorial. .

  1. In Edge UI, open the proxy that 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 give the script a name, like js-example.
  5. Paste the following code in the code editor and save the proxy. The important thing to notice is the context object. This object is available to the JavaScript code anywhere in the proxy flow. It's used to obtain flow-specific constants, to call useful get/set methods, and for more operations. This object part is of Edge's JavaScript object model. Note, too, that the target.url flow variable is a built-in, read/write variable that is accessible in the Target Request flow. When we set that variable with the API URL, Edge makes its backend call to that URL. We've essentially rewritten the original target URL, which was whatever you specified when you created the proxy (e.g., 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. Give the policy a name, like target-rewrite. Accept the defaults, and save the policy.
  8. If you select the Proxy Endpoint Preflow in the Navigator, you'll see that the policy was added to that flow.
  9. In the Navigator, select the Target Endpoint PreFlow icon.
  10. From the Navigator, drag the JavaScript policy onto the Request side of the Target Endpoint in the flow editor.
  11. Save.
  12. Call the API like this, substituting your correct org name and proxy name as appropriate:
curl -i -H 'Content-Type: application/x-www-form-urlencoded' -X POST -d 'user=Will' http://myorg-test.apigee.net/js-example

One final thing, let's take a look at the XML definition for the JavaScript policy used in this example. The important thing to note is that the <ResourceURL> element is used to speicfy the JavaScript source file to execute. This same pattern is used for any JavaScript source file: jsc://filename.js. If you're JavaScript code requires includes, you can use one or more <IncludeURL> elements to do that, as described later in this reference.

<?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 configuration, then retrieve the element's value with JavaScript at runtime.

Use the element's name attribute to specify the name with which to access the property from JavaScript code. The <Property> element's value (the value between the opening and closing tags) is the literal value that will be received by the JavaScript.

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

  • Configure the property. Here, 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 with JavaScript. Here, the retrieved value -- a variable name -- is then used by the getVariable function 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 that you can use in a JavaScript callout, see this post in the Apigee Community. Suggestions offered in the Apigee Community are for information only and do not necessarily represent best practices recommended by Apigee.


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>
</Javascript>

<Javascript> Attributes

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

The following attributes are specific to this policy.

Attribute Description Default Presence
timeLimit

Specifies the maximum time (in milliseconds) that the script is permitted to execute.

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.

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 be loaded as dependency to the main JavaScript file specified with the <ResourceURL> element. The scripts will be evaluated 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 with additional <IncludeURL> elements.

<IncludeURL>jsc://my-javascript-dependency.js</IncludeURL>
Default: None
Presence: Optional
Type: String

Example

See the Basic Example in the Samples section.

<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 will execute 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), or at the organization or environment scopes for reuse across multiple API proxies, as described in Resource files. Your code can use the objects, methods, and properties of the JavaScript object model.

<ResourceURL>jsc://my-javascript.js</ResourceURL>
Default: None
Presence: Required
Type: String

Example

See the Basic Example in the Samples section.

<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 that you use to configure TLS for a TargetEndpoint/TargetServer. See Configuring TLS from Edge to the backend for more information.

For more infomration on creating HTTP clients, see Implementing HTTP clients in JavaScript.

Usage notes

A JavaScript policy contains no actual code. Instead, a JavaScript policy references a JavaScript 'resource' and defines the Step in the API flow where the JavaScript executes. You can upload your script through the Management UI proxy editor, or you can include it in the /resources/jsc directory in API proxies that you develop locally.

Debugging JavaScript policy code

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

To view print statements in Trace:

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

  4. Your print statements will appear in this panel.

You can use the print() function to output debug information to the Trace tool. This function is available directly through the JavaScript object model. For details, see "Debug JavaScript with print() statements".

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. A typical pattern looks like this:

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

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

Error reference

This section describes the fault codes and error messages that are returned and fault variables that are set by Edge 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.

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. build
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.

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. build
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. build
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). build
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. build

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

{
  "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

Apigee Community articles

You can find these related articles on the Apigee Community: