Readarr/UI/Instrumentation/StringFormat.js

'use strict';
String.prototype.format = function () {
    var args = arguments;
    return this.replace(/{(\d+)}/g, function (match, number) {
        if (typeof args[number] !== 'undefined') {
            return args[number];
        } else {
            return match;
        }
    });
};