Amazon API Gateway
Developer Guide

Simple Calculator Lambda Function

As an illustration, we will use a Node.js Lambda function that performs the binary operations of addition, subtraction, multiplication and division.

Simple Calculator Lambda Function Input Format

This function takes an input of the following format:

{ "a": "Number", "b": "Number", "op": "string"}

where op can be any of (+, -, *, /, add, sub, mul, div).

Simple Calculator Lambda Function Output Format

When an operation succeeds, it returns the result of the following format:

{ "a": "Number", "b": "Number", "op": "string", "c": "Number"}

where c holds the result of the calculation.

Simple Calculator Lambda Function Implementation

The implementation of the Lambda function is as follows:

console.log('Loading the Calc function'); exports.handler = function(event, context, callback) { console.log('Received event:', JSON.stringify(event, null, 2)); if (event.a === undefined || event.b === undefined || event.op === undefined) { callback("400 Invalid Input"); } var res = {}; res.a = Number(event.a); res.b = Number(event.b); res.op = event.op; if (isNaN(event.a) || isNaN(event.b)) { callback("400 Invalid Operand"); } switch(event.op) { case "+": case "add": res.c = res.a + res.b; break; case "-": case "sub": res.c = res.a - res.b; break; case "*": case "mul": res.c = res.a * res.b; break; case "/": case "div": res.c = res.b===0 ? NaN : Number(event.a) / Number(event.b); break; default: callback("400 Invalid Operator"); break; } callback(null, res); };

Create the Simple Calculator Lambda Function

You can use the AWS Lambda console at to create the function, pasting the above code listing into the online code editor as follows.

                  Create the SimpleCalc Lambda function in Node.js