let and const are good practice in code that will be transpiled, or in Node.js, but they're newish features that don't have 100% browser support yet, so they sh

let and const are good practice in code that will be transpiled, or in Node.js, but they're newish features that don't have 100% browser support yet, so they shouldn't be used if your code has to run directly in a browser. https://caniuse.com/#feat=let https://caniuse.com/#feat=let