A utility for Amazon DynamoDb Data Types for AWS SDK for Node.js.


A utility for Amazon DynamoDB data types.

This utility is designed for the Amazon SDK for Node.js. It helps represent AWS DynamoDb data types.

Following are some key-value pairs:

var data = { 
  name: 'Java Script',
  age: 18,
  fav: {
    food: ['Rice', 'Noodles'],
    colors: ['Orange', 'Blue']
  engines: [ 'Rhino', 'v8', 'SpiderMonkey', 'Carakan', 'JavaScriptCore' ]

In order to put the above data into DynamoDB, the AWS SDK requires it to be represented as:

  "name": { "S": "Java Script" },
  "age": { "N": "18" },
  "fav": { 
    "M": {
      "food": { "SS": [ "Rice", "Noodles" ] },
      "colors": { "SS": ["Orange", "Blue" ] }
  "engines": { "SS": ["Rhino", "v8", "SpiderMonkey", "Carakan", "JavaScriptCore" ] }

This utility helps to construct such representations required by the AWS SDK for Node.js

To represent the above var data as a DynamoDB AttributeValue do:

var attr = require('dynamodb-data-types').AttributeValue;
// { 
//   "name": { "S": "Java Script" }, 
//   "age": { "N": "18" }, 
//   "fav": {  
//     "M": { 
//       "food": { "SS": [ "Rice", "Noodles" ] }, 
//       "colors": { "SS": ["Orange", "Blue" ] } 
//     } 
//   }, 
//   "engines": { "SS": ["Rhino", "v8", "SpiderMonkey", "Carakan", "JavaScriptCore" ] } 
// } 
var attr = require('dynamodb-data-types').AttributeValue;
var infoAttrValue = attr.wrap({ name: "Foo", age: 50 });
// {"name":{"S":"Foo"},"age":{"N":"50"}} 
var experience = {
  count: {"N": "4" },
  languages: { "SS": ["Java Script", "Ruby", "GLSL", "C" ] }
// {"count":4,"languages":["Java Script","Ruby","GLSL","C"]} 

Refer to docs.aws.amazon.com/amazondynamodb/latest/APIReference/API_Types.html

DynamoDb-Data-Types supports:

  • AttributeValue
  • AttributeValueUpdate

Refer to docs.aws.amazon.com/amazondynamodb/latest/APIReference/API_AttributeValue.html

DynamoDb-Data-Types supports:

  • B
  • BOOL
  • BS
  • L
  • M
  • N
  • NS
  • NULL
  • S
  • SS

Its trivial to detect N, NS, S, SS, NULL and BOOL. The other types M, L, B, BS are not difficult but need some explaining.

For any a given value val, wrap() detects the AWS Data types as follows:

How wrap() detects them (psuedo-code):

IF val is typeof boolean
    THEN detect as type BOOL
ELSE IF val is null
    THEN detect as type NULL
ELSE IF val is typeof number or if val instanceof Number
    THEN detect as type N
ELSE IF val is typeof string or if val is instanceof String
    THEN detect as type S

How wrap() detects type B (psuedo-code):

IF val is instanceof Buffer
    THEN detect as type B

There maybe other type which should get detected as B. Please let me know if you have suggestions.

How wrap() detects type M (psuedo-code):

IF (val is none of: BOOL, NULL, N, S, B)
    AND (typeof val === 'object')
        THEN detect as type M
    wrap() ignores val

When wrap() sees an Array, here's what it does (psuedo-code):

IF val is an Array
    IF (every element in Array is type N)
        THEN detect as type NS
    ELSE IF (every element in Array is type S)
        THEN detect as type SS
    ELSE IF (every element in Array is type B)
        THEN detect as type BS
        detect as type L

The source is available for download from github.com/kayomarz/dynamodb-data-types.

To install using Node Package Manager (npm):

npm install dynamodb-data-types

Consider the following:

var data = {
  alphabets: ['c', 'a', 'b', 'c']

wrap(data) detects alphabets as SS. Being a set SS has two properties unlike those of arrays :

  • The order of the elements is not preserved.
  • Duplicate elements are not allowed.

Starting with version 2.1.0, you can do:

  • wrap(data, {types: {alphabets: 'L'} } to explicitly tell wrap to treat it L instead of the auto-detected SS. Similarly for put() and add()
  • Alternatively, call preserveArrays() to consider all arrays as type L. This has a global effect.

Read the documentation and examples for more.

DynamoDb-Data-Types version 2.0.0 introduces support for AttributeValue types BOOL, NULL, M, L.

DynamoDb-Data-Types uses M to nest objects. Consider the following data:

var data = {
  polygon: {
    quadrilateral: {
        sides: 4

wrap() represents the above data as follows:

  "polygon": {
    "M": {
      "quadrilateral": {
        "M": {
          "sides": {
            "N": "4"

DynamoDb-Data-Types uses L to represent mixed arrays. Consider the following data:

  strs: ['abc', 'def'],
  nums: [123, 456],
  mix: [1, 'abc', true, false, null, [1,2,3]]

wrap() represents the above data as follows:

  strs: { 
    SS: ["abc","def"] 
  nums: { 
    NS: ["123","456"] 
  mix: {
    "L": [
      { N: "1" },
      { S: "abc" },
      { BOOL: true },
      { BOOL: false },
      { NULL: true },
      { NS: ["1","2","3"] }

Read this only if you need DynamoDb-Data-Types version 1.0.0 or below.

If you are already using version 1.0.0 or 0.2.7 you may continue to do so.

If you are using DynamoDb-Data-Types version 1.0.0 or 0.2.7, wrapping / unwrapping B and BS will not work when used with AWS SDK 1.x.x but should automagically work with AWS SDK 2.x.x. although it has not been tested. This is related to automatic conversion of base64 done by AWS SDK version 2.x. See AWS Upgrading Notes (1.x to 2.0).

If preserveArrays() is called, all arrays found in the object being wrapped are given type L. In other words, arrays will no longer get detected as NS, SS or BS but specified as L.

This is useful to preserve duplicates in arrays as well as the order array elements.

var ddt = require('dynamodb-data-types');

This function is designed to be called once at the start and has a global effect.

If this is not needed on a global level, a similar effect can be achieved using options parameter passed to wrap(), wrap1() and put() and add().

Similarly, the global behaviour of preserveArrays() may be overridden using the options object passed to wrap(), wrap1() and put() and add().

AWS API Reference - AttributeValue

AWS API Reference - AttributeValueUpdate

Wrap object properties into DynamoDB's AttributeValue data type.

  • @param {Object} item The object to wrap.
  • @param {Object} options
  • @return {Object} A DynamoDb AttributeValue.
  • types: An object containing attribute names and explicit type for that attribute. Currently explicit type can only be specified if the detected type is an array. Possible values are 'NS', 'SS', 'BS', 'L'

Example of an options object:

// Any property named 'randomList' found in the object (at any depth) is specified as 'NS'. This explicit type can be assigned only if `randomList` is detected as an array. 
// Similarly if 'orderedList' is an array, it gets specified as type 'L' 
  types: {
     randomList: 'NS', 
     orderedList: 'L'


var attr = require('dynamodb-data-types').AttributeValue;
attr.wrap({name: "Foo", age: 50});
// {"name":{"S":"Foo"},"age":{"N":"50"}} 
attr.wrap({alphabets: ["a", "b", "c"]});
// {"alphabets":{"SS": ["a","b","c"]}} 
attr.wrap({alphabets: ["a", "b", "c"]}, {types: {alphabets:"L"}});
// {"alphabets":{"L": [{"S":"a"},{"S":"b"},{"S": "c"}]}} 

Unwrap DynamoDB AttributeValue to values of the appropriate types.

  • @param {Object} attributeValue The DynamoDb AttributeValue to unwrap.
  • @return {Object} Unwrapped object with properties.


var attr = require('dynamodb-data-types').AttributeValue;
// {name: "Foo", age: 50} 

Wrap a single value into DynamoDB's AttributeValue.

  • @param {String|Number|Array}
  • @param {Object} options Same as options for wrap().
  • @return {Object} DynamoDB AttributeValue.


var attr = require('dynamodb-data-types').AttributeValue;
attr.wrap1(50);    // {"N":"50"} 
attr.wrap1("50");  // {"S":"50"} 

Unwrap a single DynamoDB's AttributeValue to a value of the appropriate javascript type.

@param {Object} attributeValue The DynamoDB AttributeValue. @return {String|Number|Array} The javascript value.


var attr = require('dynamodb-data-types').AttributeValue;
attr.unwrap1({"N":"50"});  // 50 
attr.unwrap1({"S":"50"});  // "50" 

Append attributes to be updated with action "ADD". This function can be chained with further calls to add, put or delete.

  • @param {Object} attrs Object with attributes to be updated.
  • @param {Object} options Same as options for wrap().
  • @return {Updates} Object with all update attributes in the chain.

Example - put, add, delete.

See note: duplicate attribute names

Append attributes to be updated with action "PUT". This function can be chained with further calls to add, put or delete.

  • @param {Object} attrs Object with attributes to be updated.
  • @param {Object} options Same as options for wrap().
  • @return {Updates} Object with all update attributes in the chain.

Example - put, add, delete.

See note: duplicate attribute names

Append attributes to be updated with action "DELETE". This function can be chained with further calls to add, put or delete.

  • @param {Object|String|Array} attrs If this argument is an an Object,the Object's property values must be an array, containing elements to be removed, as required by DynamoDb SDK. If this argument is a String, it should contain comma seperated names of properties to be deleted. If its an Array, each array element should be a property name to be deleted.

  • @return {Updates} Object with all update attributes in the chain.

See note: duplicate attribute names

var attrUpdate = require('dynamodb-data-types').AttributeValueUpdate;
var dataUpdate = attrUpdate
    .put({name: "foo"})
    .add({age: 1})
    .delete("height, nickname")
    .add({favColors: ["red"]})
    .delete({favNumbers: [3]});
// { 
//   "name": { "Action": "PUT", "Value": { "S": "foo" } }, 
//   "age": { "Action": "ADD", "Value": { "N": "1" } }, 
//   "height": { "Action": "DELETE" }, 
//   "nickname": { "Action": "DELETE" }, 
//   "favColors": { "Action": "ADD", "Value": { "SS": ["red" ] } }, 
//   "favNumbers": { "Action": "DELETE", "Value": { "NS": ["3"] } } 
// } 

Each attribute name can appear only once in the AttributeUpdates object of the itemUpdate call. This is a feature of the AWS API. However its easy to overlook this when chaining add, put and delete updates.

For example, following is an attribute colors of type SS (String set)

var item = {
    id: ...,
    colors: ["red", "blue"]

Suppose, we want to delete "red" and add "orange".

To add "orange", the AttributeUpdates object is created as: attrUpdate.add({colors: ["orange"]}). Similarly, to delete "red" the AttributeUpdates object is created as attrUpdate.delete({colors: ["red"]})

However, both actions cannot be represented in the same AttributeUpdates object.

// Will not work as expected 
attrUpdate.add({colors: ["orange"]}).delete({colors: ["red"]});

The action to delete "red" overwrites the action to add "orange". This is simply because colors is a property of the AttrubuteUpdates object.

The following code demonstrates the above note:

JSON.stringify(attrUpdate.add({colors: ["orange"]}));
JSON.stringify(attrUpdate.delete({colors: ["red"]}));
// The below does not work as expected 
JSON.stringify(attrUpdate.add({colors: ["orange"]}).delete({colors: ["red"]}));

If you are using AWS SDK for JavaScript version 1.x.x, you should use DynamoDb-Data-Types version 1.0.0.

It is upto the application to ensure that the application follows the SDK requirements. This utility does not perform any checks.

This utility is designed for Node.js. For use in the browser, it will need to be adapted. This is in lieu of the October 2013 Developer Preview - AWS SDK for JavaScript in the Browser

To adapt this utility for the browser, following are few todos. (This list is not exhaustive)

  • Ensure browser compatibility of functions which iterate over objects. Currently lib/util.js has a function to iterate over object properties which is sufficient for use with Node.js.
  • Browser compatible ways to detect array Array.
  • Ways to detect binary data commonly used by browser applications. For instance, currently for Node.js, wrap() detects Buffer as binary type B.

Change log


  • Call preserveArrays() to use type L for array types; this preserves order of array elements and allows duplicate array elements both of which are not possible using sets SS, NS or BS
  • If not required on a global scale (calling preserveArrays), explicity set array types by passing opts to wrap(), add(), put()


  • Fixed README
  • Committed modified package.json (just realised it wasn't committed)


  • Implemnted M
  • Implemented L
  • Added example to put and get binary data (examples/02-binary-image.js)


Note: There are no source code changes in version 1.0.0. Functionally, 1.0.0 is identical to 0.2.7.

  • Bumped from version 0.2.7 to version 1.0.0.
  • Update documentation especially with regard to B and BS data types.
  • Added development deps into pacakge.json instead of tests/package.json (It should have been this way to begin with)




Note: Change log dates are yyyy-mm-dd.