javascript variable cannot been redeclared but cannot been accesed, too

Question

I'm a newcomer in Javascript. I have two files with js code. file a.js contains

const words = ["Alpha", "Bita", "Gama"];
console.log(words);

file b.js contains

//@ts-check
const words = ["Alpha", "Bita", "Gama"];
console.log(words);

Both a.js and b.js are located in folder src under the root In the root, I also have a jsconfig.json

{
    "compilerOptions": {
        "outDir": "./built",
        "module": "commonjs",
        "target": "es6",
       
    },
    "exclude": [
        "node_modules",
        "**/node_modules/*"
    ]
}

In file b.js, I receive an error "Cannot redeclare block-scoped variable 'words'." When I comment out the declaration of words in b.js, I don't receive any error, but when running file b.js, I receive a "ReferenceError: words is not defined".

I know that erasing the //@ts-check in b.js will fix the problem, but I cannot understand why type checking produces this behaviour. What is the meaning to keep a variable in scope if you are not allowed to access it? I use Visual Studio Code and run with node.