Object.entries() can be used to convert an object into a key/value pair in the form of an array. That means your object will be converted into a 2D array (at the simplest level), with each element being another array containing a key and value. Take a look at this:

const obj = {
    book: "Learning ES2017 (ES8)",
    author: "Mehul Mohan",
    publisher: "Packt",
    useful: true
};
console.log(Object.entries(obj));

The output will be:

[["book","Learning ES2017 (ES8)"],["author","Mehul Mohan"],["publisher","Packt"],["useful",true]]