How can I grep/pipe/redirect the output of tsc (TypeScript compiler)?

Question

My project consists of a very simple index.ts:

const answer: 42 = 43;

If I compile it, I get an expected type error (with colors; not shown here):

$ tsc
index.ts:1:7 - error TS2322: Type '43' is not assignable to type '42'.

1 const answer: 42 = 43;
        ~~~~~~


Found 1 error.

Let's say I want to grep for type errors:

$ tsc | grep "const answer"

I get no results. And no wonder:

$ tsc | wc -l
1
$ tsc | cat
index.ts(1,7): error TS2322: Type '43' is not assignable to type '42'.

Redirecting doesn't help:

$ tsc 2>&1 | wc -l
1
$ tsc 2>&1 | cat
index.ts(1,7): error TS2322: Type '43' is not assignable to type '42'.

How can I access the complete output of tsc in the terminal?

Answer 1

Use the --pretty flag:

$ tsc --pretty | grep "const answer"
1 const answer: 42 = 43;

(Note that "--pretty output is not meant to be parsed", so use with care.)

It works like this:

$ tsc --pretty false
index.ts(1,7): error TS2322: Type '43' is not assignable to type '42'.
$ tsc --pretty true
index.ts:1:7 - error TS2322: Type '43' is not assignable to type '42'.

1 const answer: 42 = 43;
        ~~~~~~


Found 1 error.

It's enabled by default, "unless piping to another program or redirecting output to a file".

You can also specify it in your tsconfig.json:

{
    "compilerOptions": {
        "pretty": true,
    },
}