Before You File a Proposal Please Confirm You Have Done The Following...

• I havesearched for related issues and found none that match my proposal.
• I have searched thecurrent extension rule list and found no rules that match my proposal.
• I haveread the FAQ and my problem is not listed.

My proposal is suitable for this project

• My proposal specifically checks TypeScript syntax, or it proposes a check that requires type information to be accurate.
• I believe my proposal would be useful to the broader TypeScript community (meaning it is not a niche proposal).

Link to the base rule

https://eslint.org/docs/latest/rules/no-var

Description

Typescript global declarations are more subtle than I ever expected. For a better understanding, I recommend these SO answers:

• Create a global variable in TypeScript
• Using globalThis in Typescript

Here are some key takeaways. If you want to add properties toglobalThis:

1. When the typescript file has noimport orexport keyword (i.e., it's a script, not a module), it is done like so:declare var age: number.
2. When the typescript file does haveimport orexport, you write this instead:

   // an import / export linedeclare global{varage:number;}

Ifconst orlet is used instead ofvar,globalThis.age = 18 would error in both scenarios. So if the intention is to declareglobalThis.age, it isnecessary to use thevar keyword: usingconst orlet would be a mistake. When enabled, the baseno-var rule indiscriminately marks allvar usage as wrong, but in this case, it is required.

Fail

/*eslint no-var: "error"*/export{}varx="y";varCONFIG={};

Pass

export{}declare global{varage:number;}

Additional Info

No response