ensure-key/Ensure.ts

Safe member access with initial value assignment.

// Safe member access with initial value: 
// --------------------------------------
// import './Ensure'; 
// const registry = {}; 
// registry.ensure('abc', {}).ensure('items', []).push(123);  // --> { abc: { items: [ 123 ] } }

declare interface Object {
    /** Safe member access (adds the specified key if not present and assigns the specified initial value). Returns the member's value. */
    ensure<TValue>(memberKey: any, initialValue: TValue): TValue; 
}

Object.prototype.ensure = function <TValue>(memberKey: any, initialValue?: TValue): TValue { 
    return this.hasOwnProperty(memberKey) ? this[memberKey] : (this[memberKey] = initialValue); 
}; 

/** Best to hide this method from enumeration with for (var m in obj), since some environments run into problems when custom methods suddenly appear on objects (e.g. Office integration in SharePointOnline): */
Object.defineProperty(Object.prototype, "ensure", { enumerable: false, writable: false, configurable: false });