Append a new object to a JSON Array in DynamoDB using NodeJS

Use list_append() and if_not_exists() together in an UpdateExpression to append to a potentially non-existent list column:

var AWS = require('aws-sdk')
var DB = new AWS.DynamoDB.DocumentClient()

function appendMarkedLocation (personId, location) {
  return DB.update({
    TableName: 'people',
    Key: { id: personId },
    ReturnValues: 'ALL_NEW',
    UpdateExpression: 'set #markedLocations = list_append(if_not_exists(#markedLocations, :empty_list), :location)',
    ExpressionAttributeNames: {
      '#markedLocations': 'markedLocations'
    },
    ExpressionAttributeValues: {
      ':location': [location],
      ':empty_list': []
    }
  }).promise()
}

appendMarkedLocation('somePeronId', {
  latitude: '22.11',
  longitude: '22.55',
  name: 'Ocean',
  description: 'Ocean',
  placeid: '32423423',
  image: 'url/icean.png'
}).then(console.log)