Add and/or overwrite values in a DynamoDB table with the Document Client

index.js

const AWS = require('aws-sdk')

const docClient = new AWS.DynamoDB.DocumentClient()

const mapKeys = (input, transform) => {
  const output = {}
  Object.keys(input).forEach((key, index, array) => {
    output[transform(key, index, array)] = input[key]
  })
  return output
}

const generateNames = (input) => {
  const output = {}
  Object.keys(input).forEach((key, index) => {
    output[`#${index}`] = key
  })
  return output
}

const updateExpressions = (update) => {
  const names = generateNames(update)
  const values = mapKeys(update, (_, index) => `:${index}`)
  const expressions = Object.keys(update).map((key, index) => {
    return `#${index}=:${index}`
  })
  const expression = `SET ${expressions.join(', ')}`
  return {
    ExpressionAttributeNames: names,
    ExpressionAttributeValues: values,
    UpdateExpression: expression,
  }
}

const update = async (table, hashKey, rangeKey, update) => {
  const updates = updateExpressions(update)
  const params = {
    TableName: table,
    Key: {
      hashKey,
      rangeKey,
    },
    ...updates,
  }
  await docClient.update(params).promise()
}

Let me know if you want me to turn this into an npm package.