# Use a JavaScript SDK generated by API Gateway for a REST API
<a name="how-to-generate-sdk-javascript"></a>

The following procedure shows how to use a JavaScript SDK generated by API Gateway.

**Note**  
These instructions assume you have already completed the instructions in [Generate SDKs for REST APIs in API Gateway](how-to-generate-sdk.md).

**Important**  
If your API only has ANY methods defined, the generated SDK package will not contain an `apigClient.js` file, and you will need to define the ANY methods yourself.

**To install, initiate and call a JavaScript SDK generated by API Gateway for a REST API**

1. Extract the contents of the API Gateway-generated .zip file you downloaded earlier.

1. Enable cross-origin resource sharing (CORS) for all of the methods the SDK generated by API Gateway will call. For instructions, see [CORS for REST APIs in API Gateway](how-to-cors.md).

1. In your web page, include references to the following scripts.

   ```
   <script type="text/javascript" src="lib/axios/dist/axios.standalone.js"></script>
   <script type="text/javascript" src="lib/CryptoJS/rollups/hmac-sha256.js"></script>
   <script type="text/javascript" src="lib/CryptoJS/rollups/sha256.js"></script>
   <script type="text/javascript" src="lib/CryptoJS/components/hmac.js"></script>
   <script type="text/javascript" src="lib/CryptoJS/components/enc-base64.js"></script>
   <script type="text/javascript" src="lib/url-template/url-template.js"></script>
   <script type="text/javascript" src="lib/apiGatewayCore/sigV4Client.js"></script>
   <script type="text/javascript" src="lib/apiGatewayCore/apiGatewayClient.js"></script>
   <script type="text/javascript" src="lib/apiGatewayCore/simpleHttpClient.js"></script>
   <script type="text/javascript" src="lib/apiGatewayCore/utils.js"></script>
   <script type="text/javascript" src="apigClient.js"></script>
   ```

1. In your code, initialize the SDK generated by API Gateway by using code similar to the following.

   ```
   var apigClient = apigClientFactory.newClient();
   ```

   To initialize the SDK generated by API Gateway with AWS credentials, use code similar to the following. If you use AWS credentials, all requests to the API will be signed. 

   ```
   var apigClient = apigClientFactory.newClient({
     accessKey: 'ACCESS_KEY',
     secretKey: 'SECRET_KEY',
   });
   ```

   To use an API key with the SDK generated by API Gateway, pass the API key as a parameter to the `Factory` object by using code similar to the following. If you use an API key, it is specified as part of the `x-api-key` header and all requests to the API will be signed. This means you must set the appropriate CORS Accept headers for each request.

   ```
   var apigClient = apigClientFactory.newClient({
     apiKey: 'API_KEY'
   });
   ```

   

1. Call the API methods in API Gateway by using code similar to the following. Each call returns a promise with a success and failure callbacks.

   ```
   var params = {
     // This is where any modeled request parameters should be added.
     // The key is the parameter name, as it is defined in the API in API Gateway.
     param0: '',
     param1: ''
   };
   
   var body = {
     // This is where you define the body of the request,
   };
   
   var additionalParams = {
     // If there are any unmodeled query parameters or headers that must be
     //   sent with the request, add them here.
     headers: {
       param0: '',
       param1: ''
     },
     queryParams: {
       param0: '',
       param1: ''
     }
   };
   
   apigClient.methodName(params, body, additionalParams)
       .then(function(result){
         // Add success callback code here.
       }).catch( function(result){
         // Add error callback code here.
       });
   ```

   Here, the *methodName* is constructed from the method request's resource path and the HTTP verb. For the SimpleCalc API, the SDK methods for the API methods of 

   ```
   1. GET /?a=...&b=...&op=...
   2. POST /
   
      { "a": ..., "b": ..., "op": ...}
   3. GET /{a}/{b}/{op}
   ```

   the corresponding SDK methods are as follows:

   ```
   1. rootGet(params);      // where params={"a": ..., "b": ..., "op": ...} is resolved to the query parameters
   2. rootPost(null, body); // where body={"a": ..., "b": ..., "op": ...}
   3. aBOpGet(params);      // where params={"a": ..., "b": ..., "op": ...} is resolved to the path parameters
   ```