Array#join Override

index.ts

//#region Types

// Just here to validate that the new signature is identical to the es5 type declaration
type Array$join$primordial_Signature = (separator?: string) => string

declare interface Array<T>
{
    separator?:       string;

    join:             Array$join$primordial_Signature;
    join$$primordial: Array$join$primordial_Signature
}

//#endregion Types

//#region Variables

// Store original method
const Array$join$primordial: Array$join$primordial_Signature = Array.prototype.join;

// Absolute fallback for separator (same as original prototype method)
let originalSeparator = ',';
// New configurable separator parameter default value
let defaultSeparator = ' ';

//#endregion Variables

//#region New `join`

function Array$join(this: Array<any>, separator?: string): string
{
    return Array$join$primordial.bind(this)(separator ?? this.separator ?? originalSeparator);
}

//#endregion New `join`

//#region Binder

function bindBuiltinExtension()
{
    // Array.prototype.separator = defaultSeparator
    // Array.prototype.join      = Array$join;
    Object.assign(Array.prototype, {
        separator:        defaultSeparator,
        join:             Array$join,
        join$$primordial: Array$join$primordial
    })
};

//#endregion Binder