Dangerous "name" (and potentially others) global

TypeScript Version: 2.6.0-dev.20170913

Code

if (name === "asdf") {
  console.log("asdf")
}

https://www.typescriptlang.org/play/#src=if (name %3D%3D%3D "asdf") {%0D%0A console.log('hello')%0D%0A}

Expected behavior:

Error out

Actual behavior:

More than once, I had a “local” variable called name, outside a block scope, and it didn’t warn me that it’s not defined (or used before declaration). even though, in my code, event.name is a string, the global name variable is of type never. it’s defined in lib.dom.d.ts, along with other “juicy” global names that will provide some confusion, like length, external, event, closed

one ‘fix’ (that would be a breaking change) would to make lib.dom-globals.d.ts (the propertiers that are usually accessible through window variable) and make it an opt-in in tsconfig.json compilerOptions.lib array

[ericanderson]

Perhaps we could get a compiler flag for noImplicitGlobalThis? Thus using name would be an error but if you want to use globalThis.name you could?

[mhegazy]

I think we are just trying to be too clever here. just remove the damn thing 😃