JSFiddle - React, Tailwind, and code Playground

JavaScript

alert(keys({
    a: 1,
    b: 2,
    c: 3,
    d: 4,
    e: 5,
    f: function () {}
}));

function keys(obj) {
    var hasOwnProperty = Object.prototype.hasOwnProperty;

    var properties = [];

    for (var property in obj)
        if (hasOwnProperty.call(obj, property)
            && typeof obj[property] !== "function")
                properties.push(property);

    return properties;
}