List All Methods of an Object in JavaScript

const getMethods = obj => {
    let properties = new Set();
    let currentObj = obj;
    do {
        Object.getOwnPropertyNames(currentObj).map(item =>
            properties.add(item)
        );
    } while ((currentObj = Object.getPrototypeOf(currentObj)));
    return [...properties.keys()].filter(
        item => typeof obj[item] === "function"
    );
};

//
// Example usage:
//

getMethods("");
getMethods(new String("test"));
getMethods({});
getMethods(Date.prototype);