ES6 and Beyond by Laurie Barth

• Flatten a Nested Array in JavaScript with Array.prototype.flat
• Convert an Object to an Array and back again with Object.entries and Object.fromEntries
• Copy an Array with the Spread Operator
• Copy an Object with the Spread Operator
• Merge Arrays using the Spread Operator
• Merge Objects with JavaScript's Spread Operator
• Array.prototype.flatMap from ES2019
• For...in Loop vs. For...of Loop
• Nested Destructuring for Objects
• Safely Access a Property on a JavaScript Object with Optional Chaining
• Safely Access a Property on a JavaScript Array with Optional Chaining