Looping Over Items With for...of

Looping Over Items With for…of

In this lesson, you ported the first loop of the night-bus report from Python to JavaScript.

• Python’s for delay in delays: becomes for (const delay of delays) { ... }. The word is of, parentheses wrap the header, and braces mark the body, because JavaScript doesn’t read indentation.
• You always declare the loop variable. Python’s assignment creates a name; JavaScript keeps declaring (const or let) and assigning apart.
• Leaving out the declaration, as you would in Python, is a ReferenceError in an ES module. The "type": "module" in your project’s package.json makes every .js file in your project an ES module, and ES modules always run in strict mode.
• Strict mode turns some silent mistakes, like this one, into errors. Under the older “sloppy” rules, the assignment would quietly create a global variable, even inside a function, where Python would keep the name local. Those rules still apply to the REPL and to CommonJS, Node’s older module format: a .js file that uses require() in a project without "type": "module", or any .cjs file.
• const works because JavaScript creates a fresh variable on every pass and sets it once, where Python rebinds one name on every pass. let works too, but const is what JavaScript developers write when the body doesn’t reassign it.
• for...of works on strings too, one character per pass, as Python’s for does.

The finished code:

const delays = [4, 0, 12];
for (const delay of delays) {
  console.log(delay);
}