// A *self-contained* demonstration of the problem follows...
// Test this by running `tsc` on the command-line, rather than through another build tool such as Gulp, Webpack, etc.

interface MimeTypeArray {
    readonly length: number;
    item(index: number): MimeType;
    namedItem(type: string): MimeType;
    [index: number]: MimeType;
}

interface MimeTypeArray {
    readonly length: number;
    item(index: number): Plugin;
    namedItem(type: string): Plugin;
    [index: number]: Plugin;
}