@polkadot/util/object/property.js

/**
 * @name objectProperty
 * @summary Assign a get property on the input object
 */
export function objectProperty(that, key, getter, getName, index = 0) {
    const name = getName
        ? getName(key, index)
        : key;
    // There are 3 approaches here -
    //  - Object.prototype.hasOwnProperty.call(that, key) - this only checks the current class, i.e
    //    will retuirn false if the property is set in the parent class
    //  - isUndefined(...) - this may yield a false positive when the property is there, but not set.
    //    Additionally, on pre-defined getters it may make a call
    //  - key in that - Does not need to be combined with either of the above and checks the full chain
    if (!(name in that)) {
        Object.defineProperty(that, name, {
            enumerable: true,
            // Unlike in lazy, we always call into the upper function, i.e. this method
            // does not cache old values (it is expected to be used for dynamic values)
            get: function () {
                return getter(key, index, this);
            }
        });
    }
}
/**
 * @name objectProperties
 * @summary Assign get properties on the input object
 */
export function objectProperties(that, keys, getter, getName) {
    for (let i = 0, count = keys.length; i < count; i++) {
        objectProperty(that, keys[i], getter, getName, i);
    }
}