Array.prototype.onlySome - Determines whether some but not all members of an array satisfy the specified test.

onlySome.js

/**
 * Determines whether some but not all members of an array satisfy the specified test.
 *
 * @param callbackfn A function that accepts up to three arguments. The onlySome method calls
 * Array.prototype.some and Array.prototype.every. Both call the callbackfn function for each
 * element in the array until the callbackfn returns a value which is coercible to the Boolean value true
 * or false respectively, or until the end of the array.
 * @param thisArg An object to which the this keyword can refer in the callbackfn function.
 * If thisArg is omitted, undefined is used as the this value.
 * @returns {boolean}
 */
Array.prototype.onlySome = function(callbackfn, thisArg = undefined) {
    if (this === null) {
        throw new TypeError("Array.prototype.onlySome called on null or undefined");
    }
    return !this.every(callbackfn, thisArg) && this.some(callbackfn, thisArg);
}