AWS SDK for JavaScript
Developer Guide for SDK version 2.122.0

Working with JSON

JSON is a format for data exchange that is both human and machine-readable. While the name JSON is an acronym for JavaScript Object Notation, the format of JSON is independent of any programming language.

The SDK for JavaScript uses JSON to send data to service objects when making requests and receives data from service objects as JSON. For more information about JSON, see

                    Showing the general format and parts of JSON.

JSON represents data in two ways:

  • An object, which is an unordered collection of name-value pairs. An object is defined within left ({) and right (}) braces. Each name-value pair begins with the name, followed by a colon, followed by the value. Name-value pairs are comma separated.

  • An array, which is an ordered collection of values. An array is defined within left ([) and right (]) brackets. Items in the array are comma separated.

Here is an example of a JSON object that contains an array of objects in which the objects represent cards in a card game. Each card is defined by two name-value pairs, one that specifies a unique value to identify that card and another that specifies a URL that points to the corresponding card image.

var cards = [{"CardID":"defaultname", "Image":"defaulturl"}, {"CardID":"defaultname", "Image":"defaulturl"}, {"CardID":"defaultname", "Image":"defaulturl"}, {"CardID":"defaultname", "Image":"defaulturl"}, {"CardID":"defaultname", "Image":"defaulturl"}];

JSON as Service Object Parameters

Here is an example of simple JSON used to define the parameters of a call to a Lambda service object.

var pullParams = { FunctionName : 'slotPull', InvocationType : 'RequestResponse', LogType : 'None' };

The pullParams object is defined by three name-value pairs, separated by commas within the left and right braces. When providing parameters to a service object method call, the names are determined by the parameter names for the service object method you plan to call. When invoking a Lambda function, FunctionName, InvocationType, and LogType are the parameters used to call the invoke method on a Lambda service object.

When passing parameters to a service object method call, provide the JSON object to the method call, as shown in the following example of invoking a Lambda function.

lambda = new AWS.Lambda({region: 'us-west-2', apiVersion: '2015-03-31'}); // create JSON object for service call parameters var pullParams = { FunctionName : 'slotPull', InvocationType : 'RequestResponse', LogType : 'None' }; // invoke Lambda function, passing JSON object lambda.invoke(pullParams, function(err, data) { if (err) { console.log(err); } else { console.log(data); } });

Returning Data as JSON

JSON provides a standard way to pass data between parts of an application that need to send several values at the same time. The methods of client classes in the API commonly return JSON in the data parameter passed to their callback functions. For example, here is a call to the getBucketCors method of the Amazon S3 client class.

// call S3 to retrieve CORS configuration for selected bucket s3.getBucketCors(bucketParams, function(err, data) { if (err) { console.log(err); } else if (data) { console.log(JSON.stringify(data)); } });

The value of data is a JSON object, in this example JSON that describes the current CORS configuration for a specified Amazon S3 bucket.

{ "CORSRules": [ { "AllowedHeaders":["*"], "AllowedMethods":["POST","GET","PUT","DELETE","HEAD"], "AllowedOrigins":["*"], "ExposeHeaders":[], "MaxAgeSeconds":3000 } ] }