Throwing errors/response outside exports.handler - node.js

Question

I've just started using AWS Lambda/Node.JS/API Gateway with API Lambda Proxy integration, and I'm struggling with something that should be simple. Handling error from outside exports.handler.
I've developed all my code, it's all working fine, however, I'm struggling to handle errors. I'm using async/await, no callback.
Basically, my code looks like something like this:
exports.handler = async (event, context) => {
const sampleVar = await sampleFunction();
const response = {
statusCode: 200,
body: JSON.stringify(sampleVar),
isBase64Encoded: false
};
return response;
}
Great, right? My problem is that all my "real code" is being developed outside the exports.handler in different functions, something like:
async function sampleFunction() {
const test = 123;
return anotherFunction(test);
}
async function anotherFunction() {
const test2 = 'blablabla';
return test2;
}
Now, let's suppose that an error happens on my sampleFunction and I need to throw the error right away. I could just go throw { statusCode: 400, etc, etc };, however, if I throw the error, I get a "500 Internal Server Error" as my response, no matter what. I can only proper break my code if I handle the error from within my exports.handler function. In that case, I could go return { statusCode: 400, etc, etc }; or context.fail(), etc, and everything would be alright.
My question is: is there any way to "break" my code and send a proper response from outside my exports.handler? Or maybe externally call my exports.handler to return a specific response?

Answer 1

so, i would write this in the comments, but the markup is a bit poor. I would do something like the below:
exports.handler = async (event, context) => {
return await sampleFunction().then(craftOk).catch(craftErr);
}
function craftOk(res) {
return {
statusCode: 200,
body: JSON.stringify(res),
isBase64Encoded: false
};
}
function craftBad(err) {
return {
statusCode: 400,
body: err.message,
isBase64Encoded: false
}
}
for fun, I wrote a test script to validate return from catch on async/await...maybe it will help
function test(toggle) {
return (toggle) ? Promise.resolve("yay") : Promise.reject(new Error("boo"))
}
async function main1() {
let res = await test(true).then( res => {
return {
statusCode: 200,
body: res,
isBase64Encoded: false
}
})
.catch(err => {
return {
statusCode: 400,
body: err.message,
isBase64Encoded: false
}
})
return res
}
async function main2() {
let res = await test(false).then( res => {
return {
statusCode: 200,
body: res,
isBase64Encoded: false
}
})
.catch(err => {
return {
statusCode: 400,
body: err.message,
isBase64Encoded: false
}
})
return res
}
main1().then(console.log)
main2().then(console.log)