typescript-is is a library which enables type checks at run-time! This is an incredible tool to validate input and make your code more type-safe 🎉.
Validating the input of cloud functions can be a challenging problem. Re-using your types to ensure that your input matches your type solves a big part of the validation problem. To do this with the typescript-is
library, the only thing you need to do is to use the assertType
method that typescript-is
exports:
// 2. Use the `assertType` method to perform your runtime check
assertType<MyEvent>(input)
Above we use assertType
to check whether our runtime object input
matches our type MyEvent
. If it doesn't match the MyEvent
type, an error is thrown. typescript-is
has a bunch of other methods such as is
or strictEqual
. If you'd like to throw the error yourself you could do this for example:
if (!is<MyEvent>(input)) {
throw new Error('input does not match type')
}
That's pretty much all it takes to add a run-time type check of your cloud functions input (provided you are a typescript user 🙃). Whereas previously you might have reached for validation libraries such as joi or god-forbid, written your own validator, it's now just one line of code. What are you going to do with all this new-found time?
Below is the entirety of an AWS lambda function handler with this pattern applied:
import { Handler } from 'aws-lambda'
import { assertType } from 'typescript-is';
type MyEvent = {
msg: string
}
async function handler<Handler>(event: MyEvent) {
assertType<MyEvent>(event)
return { msg: 'Hello World' }
}
exports.handler = handler
🚀
For a fully working example of this pattern including deployment scripts for AWS and compilation with webpack please have a look at this boilerplate I've put together.
👍
Thanks for reading, this post was originally published on my website.
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