The FunctionalUtil class holds functional JavaScript helper methods.

FunctionalUtil.ts

export class FunctionalUtil{
    
    static removeItem<T>(arr: T[], index: number): T[]{
        return [
            ...arr.slice(0, index),
            ...arr.slice(index + 1)
        ];
    }

    static replaceItem<T>(arr: T[], item: T, index: number): T[]{
        return[
            ...arr.slice(0, index),
            item,
            ...arr.slice(index +1)
        ];
    }

    static addItem<T>(arr: T[], item: T): T[]{
        return [...arr, item];
    }
}