How to Properly Add Two Numbers in a Lambda Function with Node.js

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Understanding the Problem

In the scenario presented, the user aims to add two numbers received in an event and store the result in a DynamoDB database. However, due to the way JavaScript handles strings and numbers, adding two string values results in concatenation rather than arithmetic addition. If both event.First and event.Second are strings, the addition will yield a combined string instead of the mathematical sum.

Example of the Problem

Given:

event.First = "50"

event.Second = "50"

Expected Result: 100

Actual Result: 5050

A Step-by-Step Solution

To solve this problem, follow a straightforward process to convert the string inputs into numbers and then perform the addition correctly.

1. Convert Strings to Numbers

You need to convert the input values from strings to integers so that addition works as intended. In JavaScript, you can use parseInt() for this purpose.

2. Add the Numbers

Once you have the inputs as numbers, you can simply use the + operator to get the total.

3. Prepare the Data for DynamoDB

The result should be formatted correctly for storing in DynamoDB. Since you will be saving the total as a number, you can use the N type in DynamoDB.

Example Code Implementation

Here is how the entire code would look in your Lambda function:

[[See Video to Reveal this Text or Code Snippet]]

Summary of the Steps

Parse Input: Convert string inputs using parseInt().

Perform Addition: Use the + operator to add the two numbers.

Format Data: Create a params object for DynamoDB with the total in the correct format.

Conclusion

Next time you face a similar issue, remember this approach to easily add two numbers in your Lambda function!