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This utility helps represent AWS DynamoDb data types. It converts JavaScript objects into objects as required by DynamoDb.

For example, following is some JavaScript data:

var data = {
  fruit: 'Apple',
  count: 12

The DynamoDB SDK requires it to be represented as:

    "fruit": {
      "S": "Apple"
    "count": {
      "N": "12"

Use wrap and unwrap to convert objects form one form into the other.

Quick Example

var attr = require('dynamodb-data-types').AttributeValue;
var data = {
  id: 10,
  food: ['Rice', 'Noodles'],
  age: 1,
  isThatYou: true,
  stuff: ['Tomato', 33],
  day: 'Tuesday'
// wrap: marshall data into the format required by DynamoDb.
var dynamodbData = attr.wrap(data);
// {
//   "id": {"N": "10"},
//   "food": {"SS": ["Rice", "Noodles"] },
//   "age": {"N": "1"},
//   "isThatYou": {"BOOL": true},
//   "stuff": {"L": [{"S": "Tomato"}, {"N": "33"}]},
//   "day": {"S": "Tuesday"}
// }
// unwrap: unmarshall data back to the orignal.
var unwrapped = attr.unwrap(dynamodbData);
// {
//   "id": 10,
//   "food": ["Rice", "Noodles"],
//   "age": 1,
//   "isThatYou": true,
//   "stuff": ["Tomato", 33],
//   "day": "Tuesday"
// }
// Helper for working with DynamoDb update ('updateItem'):
var attrUpdate = require('dynamodb-data-types').AttributeValueUpdate;
var dataUpdates = attrUpdate
      .put({game: "Football"})
      .add({age: 1})
// {
//   "game": {
//     "Action": "PUT",
//     "Value": {"S": "Football"}
//   },
//   "age": {
//     "Action": "ADD",
//     "Value": {"N": "1"}
//   },
//   "day": {
//     "Action": "DELETE"
//   }
// }

The above example does not commnicate with a DynamoDb instance. It only demonstrates how to wrap / unwrap data. There are more examples below.

Incase you need to wrap/unwrap individual values, use wrap1 and unwrap1:

//{ N: '50' }

Use with Node.js

Use with AWS SDK for Node.js

npm install dynamodb-data-types

Use in cli

Use with the cli for quick utility

npm install -g dynamodb-data-types
dynamo-dt-attr-wrap '{"hello":"world"}'
dynamo-dt-attr-unwrap '{"hello": {"S": "world"}}'

Use in the browser

Use with AWS SDK for JS in the Browser

Download the browser version from dist.

See examples/browser and this note

Notes for use in the browser

The browser version of this library (created using browserify) has not been tested. Pull requests to add tests for the browser are welcome (maybe using phantom.js?).

The browser version is available from version 2.1.2 onwards.

File size of the browser version

The browser version of this library is generated using Browserify.

For versions 3.0.0 onwards of this library, browserify is made to exclude Buffer related code. It is less likely for a browser side application to make use of Buffer as a binary type.

If you don't need detailed info about this, skip the next paragraph.

This library uses node's Buffer for recognizing binary types. By default, browserify, includes external Buffer related code, causing the filesize of the browser dist to become 5.4 times larger (6x if you compare min.js files). Version 3.0.0 onwards, browserify is made to exclude Buffer related code because it seems less likely for browser side code to detect Buffer as a binary type. Incase your browser application does require Buffer you might try using dist-with-buffer



Refer to

DynamoDb-Data-Types supports:

  • AttributeValue
  • AttributeValueUpdate

Supported AttributeValue types

Refer to

DynamoDb-Data-Types supports:

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


(New in version 2.1.0)

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 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.

Support for BOOL, NULL, M, L

(new in version 2.0.0)

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

Use of M for nested data

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

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

wrap() maps the above data as:

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

Use of L for arrays

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() maps the above data as:

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

Detecting data types

It is straightforward to detect types N, NS, S, SS, NULL and BOOL. To detect other types - M, L, B, BS - simple rules are applied as explained below.

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 types 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

API - Reference documentation

Global settings


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 and the order of elements in arrays.

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

This function is designed to be called once - It 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(item[, options])

Wrap (marshall) JavaScript data 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 (unmarshall) DynamoDB AttributeValue to appropriate JavaScript 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}

wrap1(value [, options])

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"


add(attrs [, options])

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

put(attrs [, options])

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

Example: put, add, delete

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"] } }
// }

Note: Duplicate attribute names in AttributeValueUpdate

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"]}));

Older versions of DynamoDb-Data-Types

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).

Change log

Version 3.0.0

  • For Node users, version 3.0.0 is identical to 2.1.6
  • For browser side version of this library
    • In version 3.0.0 onwards Buffer related code has been excluded.
    • Filesize of the min.js version is now 6.5KB. Earlier it was 40KB.

Version 2.1.2 - 2.1.6

  • Added/fixed tests to imporve coverage.
  • Reviewed docs.

Source code of versions 2.1.2 to 2.1.6 are identical to 2.1.1.

Version 2.1.2

This version is identical to 2.1.1 with no changes to code. It only includes a JS build for the browser plus a few more tests.

  • Use browserify to create a dist for use in the browser.
  • Updated tests, use travis-ci, coverage, istanbul, .jshintrc.

Version 2.1.1


  • Replace functions deprecated by Node.

Version 2.1.0


  • 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()

Version 2.0.1


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

Version 2.0.0


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

Version 1.0.0


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)

version 0.2.7


version 0.2.6


version 0.2.5


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



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