Declaring a global array extension to check an empty list leads to a compiler error

Question

I learning Typescript and I'm trying to create convenient features with the Array extension. This example below works on the Typescript playground but my editor throws TypeError: ... is not a function. All other extensions work well but read an empty list I can't in this way. I tried many solutions from StackOverflow but it does not work anyway. Someone can explain how it works?

declare global {
    interface Array<T> {
        isNotEmpty(): boolean;
        isEmpty(): boolean;
    }
}

Array.prototype.isNotEmpty = function <T>(this: T[]): boolean {
    return !!this.length;
};

Array.prototype.isEmpty = function <T>(this: T[]): boolean {
    return !this.length;
};

export { };

Answer 1

Create a new declarations file, e.g. Array.d.ts with the declaration you're adding:

declare global {
    interface Array<T> {
        isNotEmpty(): boolean;
        isEmpty(): boolean;
    }
}

Then under the include property in your tsconfig.json add the path to that .d.ts file like so:

  "include": [
    "src/*.ts", // Or wherever your source code lies
    "Array.d.ts" // <- this is the new declaration 
  ],