How to check bitwise mask in typescript

Published on July 29, 2019

Tagged: #typescript

Follow me on twitter for more posts like this

I’m currently building a little app that talks to the Azure Devops API and I had to check a bitwise operator in typescript today. I hardly ever do this these days so it took me a bit of time to get it right!

A common use case of bit wise operators allow you to have a single field that express multiple states. It’s a 2-bit number e.g. 101, where each digit is assigned to represent a single state.

In the Azure Devops api many of the states use bitwise operators.

To test if a bit is set you will create a mask for checking. Then you can use bitwise operators to check if the real value matches the mask

// To create a mask you should OR the mask values together
var expectedStatesMask =
  ri.EnvironmentStatus.Succeeded | ri.EnvironmentStatus.InProgress

// And to check a bitwise value you need to AND the current value and your mask and check that the result matches the current status
return (
  environmentState.status === (environmentState.status & expectedStatesMask)
)
Darragh ORiordan

Hi! I'm Darragh ORiordan.

I live and work in Sydney, Australia building supporting happy teams that create high quality software for the web.

I also make tools for busy developers! Do you have a new M1 Mac to setup? Have you ever spent a week getting your dev environment just right?

My DevShell tooling will save you 30+ hours configuring your dev environment with all the best modern tools. Get it here

https://darraghoriordan.gumroad.com/l/devshell


Read more articles like this one...

List of article summaries

#typescript

How to write an ESLint plugin in TypeScript

I use NestJS at my day job. It’s a complicated framework sometimes and there are lots of things that devs “just have to remember” or there will be bugs in your application that you won’t see until runtime.

I wanted to remove this cognitive load from NestJS engineers so that they can focus on valuable work instead. I wrote an ESLint plugin to alert developers directly in their IDE or editor when these common issues exist - (Available on NPM) https://www.npmjs.com/package/@darraghor/eslint-plugin-nestjs-typed

Here is what I learned about writing ESLint plugins in typescript for typescript while building the plugin.

#typescript

Create an only ever true boolean type in typescript

Integrating with an API where a boolean can only be undefined or true I needed to type it. It’s easy enough but I just wanted to jot it down in case any one else needs this in the future.

#typescript

How to change the type of output for a property filter in typescript

If you have an iterable filter on a property in typescript you might have a slightly different model coming out of the filter based on the filter condition.

By setting the types correctly you can potentially save having to add manual typing hints in whatever follows the filter.

It’s easier to show this with code so see below!

Thanks to one of my colleagues for suggesting this one in a code review.

#typescript

Copying missing files during a typescript build on deploy

If you build your nodeJS project using typescript, it’s important to know that the typescript compiler tsc will only include files that are .js or .ts.

If you have an issue where you deploy or build a typescript project and you get a file not found issue or similar, it’s probably because you missed that typescript does not process these kinds of files for you.

If you need to include files like XML (.xml) or images in your typescript project build output, you will have to copy them manually before or after the build process.

This is one way to copy assets in a typescript build.