Copy an Array with the Spread Operator

Copy an Object with the Spread Operator

Merge Arrays using the Spread Operator

Flatten a Nested Array in JavaScript with Array.prototype.flat

Merge Objects with JavaScript's Spread Operator

For...in Loop vs. For...of Loop

Array.prototype.flatMap from ES2019

Convert an Object to an Array and back again with Object.entries and Object.fromEntries

Safely Access a Property on a JavaScript Object with Optional Chaining

Safely Access a Property on a JavaScript Array with Optional Chaining