Examples:

Get items from multiple tables

var params = {
  TransactItems: [{
    Put: {
      TableName : 'Table0',
      Item: {
        HashKey: 'haskey',
        NumAttribute: 1,
        BoolAttribute: true,
        ListAttribute: [1, 'two', false],
        MapAttribute: { foo: 'bar'},
        NullAttribute: null
      }
    }
  }, {
    Update: {
      TableName: 'Table1',
      Key: { HashKey : 'hashkey' },
      UpdateExpression: 'set #a = :x + :y',
      ConditionExpression: '#a < :MAX',
      ExpressionAttributeNames: {'#a' : 'Sum'},
      ExpressionAttributeValues: {
        ':x' : 20,
        ':y' : 45,
        ':MAX' : 100,
      }
    }
  }]
};

documentClient.transactWrite(params, function(err, data) {
  if (err) console.log(err);
  else console.log(data);
});

Calling the transactWrite operation

var params = {
  TransactItems: [ /* required */
    {
      ConditionCheck: {
        ConditionExpression: 'STRING_VALUE', /* required */
        Key: { /* required */
          '<AttributeName>': someValue /* "str" | 10 | true | false | null | [1, "a"] | {a: "b"} */,
          /* '<AttributeName>': ... */
        },
        TableName: 'STRING_VALUE', /* required */
        ExpressionAttributeNames: {
          '<ExpressionAttributeNameVariable>': 'STRING_VALUE',
          /* '<ExpressionAttributeNameVariable>': ... */
        },
        ExpressionAttributeValues: {
          '<ExpressionAttributeValueVariable>': someValue /* "str" | 10 | true | false | null | [1, "a"] | {a: "b"} */,
          /* '<ExpressionAttributeValueVariable>': ... */
        },
        ReturnValuesOnConditionCheckFailure: ALL_OLD | NONE
      },
      Delete: {
        Key: { /* required */
          '<AttributeName>': someValue /* "str" | 10 | true | false | null | [1, "a"] | {a: "b"} */,
          /* '<AttributeName>': ... */
        },
        TableName: 'STRING_VALUE', /* required */
        ConditionExpression: 'STRING_VALUE',
        ExpressionAttributeNames: {
          '<ExpressionAttributeNameVariable>': 'STRING_VALUE',
          /* '<ExpressionAttributeNameVariable>': ... */
        },
        ExpressionAttributeValues: {
          '<ExpressionAttributeValueVariable>': someValue /* "str" | 10 | true | false | null | [1, "a"] | {a: "b"} */,
          /* '<ExpressionAttributeValueVariable>': ... */
        },
        ReturnValuesOnConditionCheckFailure: ALL_OLD | NONE
      },
      Put: {
        Item: { /* required */
          '<AttributeName>': someValue /* "str" | 10 | true | false | null | [1, "a"] | {a: "b"} */,
          /* '<AttributeName>': ... */
        },
        TableName: 'STRING_VALUE', /* required */
        ConditionExpression: 'STRING_VALUE',
        ExpressionAttributeNames: {
          '<ExpressionAttributeNameVariable>': 'STRING_VALUE',
          /* '<ExpressionAttributeNameVariable>': ... */
        },
        ExpressionAttributeValues: {
          '<ExpressionAttributeValueVariable>': someValue /* "str" | 10 | true | false | null | [1, "a"] | {a: "b"} */,
          /* '<ExpressionAttributeValueVariable>': ... */
        },
        ReturnValuesOnConditionCheckFailure: ALL_OLD | NONE
      },
      Update: {
        Key: { /* required */
          '<AttributeName>': someValue /* "str" | 10 | true | false | null | [1, "a"] | {a: "b"} */,
          /* '<AttributeName>': ... */
        },
        TableName: 'STRING_VALUE', /* required */
        UpdateExpression: 'STRING_VALUE', /* required */
        ConditionExpression: 'STRING_VALUE',
        ExpressionAttributeNames: {
          '<ExpressionAttributeNameVariable>': 'STRING_VALUE',
          /* '<ExpressionAttributeNameVariable>': ... */
        },
        ExpressionAttributeValues: {
          '<ExpressionAttributeValueVariable>': someValue /* "str" | 10 | true | false | null | [1, "a"] | {a: "b"} */,
          /* '<ExpressionAttributeValueVariable>': ... */
        },
        ReturnValuesOnConditionCheckFailure: ALL_OLD | NONE
      }
    },
    /* more items */
  ],
  ClientRequestToken: 'STRING_VALUE',
  ReturnConsumedCapacity: INDEXES | TOTAL | NONE,
  ReturnItemCollectionMetrics: SIZE | NONE
};
documentclient.transactWrite(params, function(err, data) {
  if (err) console.log(err, err.stack); // an error occurred
  else     console.log(data);           // successful response
});