How to filter particular TypeScript errors in build result

Hi interwebz.
I just want to share this short poor man’s fix when migrating TypeScript to filter out some particular errors in TypeScript build.

Why the hell you (might) need it?

So what would be the common use case , why to bother mask/mute errors on build? Compile is the first test our code need to undergo, like first pass of “unit tests”.

Our situation : currently we have a lot of .js files that let’s say most of the time worked and we need to iterate on way to migrate fully from JavaScript only to TypeScript only. So we rename .js to .ts and then we ran into errors like (among others) :

1. error TS2365 Operator ‘>=’ cannot be applied to types ‘string’ and ‘number’.
2. error TS2365 Operator ‘==’ cannot be applied to types ‘string’ and ‘number’.
3.  error TS2345 Argument of type ‘number’ is not assignable to parameter of type ‘string’.

Yes indeed these are against the “logic” of TypeScript – bring types to JavaScript. But I know I want it there for some short timespan. Just to test. I don’t want to wade through 1500 same errors I know I will have to fix, but among them TypeScript also tells me big and real problems, but buried under many same errors about types.

We are not alone in this, more ppl write about it here :
https://github.com/Microsoft/TypeScript/issues/6114

https://github.com/Microsoft/TypeScript/issues/4094

https://github.com/Microsoft/TypeScript/issues/9448

and also here https://github.com/Microsoft/TypeScript/issues/11051

Solution :

So the solutions vary from custom branch of TypeScript as such to stupid grep on the command line output. And since I am on Windows 10 (my dev box) , I chose to stick with PowerShell so this is snippet that should do the job.

Lets say we want to mute TS2365 and TS2345 errors and your TS build gulp task has name someTSBuildTaskName.

PS script – output to some file :

node .\node_modules\gulp\bin\gulp.js someTSBuildTaskName --color | Select-String -NotMatch "TS2365" | Select-String -NotMatch "TS2345" | Out-File "grepts.txt"

PS script – output just to console (just drop the last part after pipe) :

node .\node_modules\gulp\bin\gulp.js someTSBuildTaskName --color | Select-String -NotMatch "TS2365" | Select-String -NotMatch "TS2345"

PS: I am calling here the gulp task without gulp installed with -g flag (global) so you can just call

gulp someTSBuildTaskName

with globally installed gulp and you are also good to go.

Found any better solution? Pls let us know in comments!

AD: you can also use this console log parser on Jenkins:

Regular Expression :

([\w\\\.]+)\((\d+),\d+\):\s+\w+\s+((?!TS2365|TS2345)\w+):\s+(.*)$

Mapping Script :

import hudson.plugins.warnings.parser.Warning

String fileName = matcher.group(1)
String line = matcher.group(2)
String category = matcher.group(3)
String message = matcher.group(4)

return new Warning(fileName, Integer.parseInt(line), "TS Error", category, message);

and plug this into your build pipeline.