Typescript: @ts-ignore Not Working on Let Variable That's Not Reassigned?

Issue

BACKSTORY (feel free to skip to the problem)

I'm trying to destructure a response from an Apollo useLazyQuery, and then change one variable. Without Typescript, it would be two simple lines:

 let [someFunction, { data, loading }] = useLazyQuery(QUERY);
 data = 'whatever'

However, that offends Typescript, because I'm making all the variables let even though most don't change. So, I changed the code to destrucure most of the response as constant, with a single exception:

 const stuff = useLazyQuery(QUERY);
 let [_, { data }] = stuff; // get one variable as a non-constant
 const [someFunction, { loading }] = stuff; // get the rest as constants

The problem is, I'm still getting TypeScript errors/warnings:

77:8 warning '_' is assigned a value but never used no-unused-vars

77:8 error '_' is never reassigned. Use 'const' instead prefer-const

Of course, _ is just a placeholder to help me destructure data, so it's not supposed to be re-assigned ... but it is needed on the let line to make the destructuring work.

PROBLEM

I would have thought I could tell Typescript "don't worry about _, just ignore it" by adding an @ts-ignore comment:

 const stuff = useLazyQuery(QUERY);
 // @ts-ignore
 let [_, { data }] = stuff; // get one variable as a non-constant
 const [someFunction, { loading }] = stuff; // get the rest as constants

But all that does is add a new warning about how I should use @ts-expect-error instead of @ts-ignore ... it doesn't get rid of the warning/error about my _ variable.

QUESTIONS (Two Related Ones)

1. I thought @ts-ignore ignored all warnings/errors on the next line; can anyone explain how Typescript decides which warnings/errors @ts-ignore actually ignores, and which it doesn't?

2. Can anyone explain how I can make Typescript stop complaining about '_' is never reassigned. Use 'const' instead error (using @ts-ignore or anything else) ... without giving up on basic language features like destructuring?

Solution

For clarification : above errors are coming from es-lint and not TS itself. You will need to disable that.

You can use:

// eslint-disable-next-line
 let [_, { data }] = stuff; 

or

 let [_, { data }] = stuff; // eslint-disable-line

Answered By - Tushar Shahi