JavaScript Lesson 1 starts a numbered BitcoinVersus.Tech JavaScript training series with the most useful building block: variables. Modern JavaScript primarily uses const and let to give values clear names and control whether those bindings can be reassigned.

const vs. let

Use const when the variable should not be reassigned. Use let when its value must change later. MDN recommends this same practical rule. Avoid var in new code unless you specifically need its older function-scoping behavior.

const minerModel = "S21";
let temperatureC = 62;

temperatureC = 64;

console.log(minerModel);
console.log(temperatureC);

Why scope matters

let and const are block-scoped. A name declared inside an if statement, loop, or other block is not automatically available outside that block.

const online = true;

if (online) {
  const status = "Miner online";
  console.log(status);
}

// console.log(status); // ReferenceError

Practical exercise

Open your browser developer console. Create a constant named siteName, a variable named activeMiners, then increase activeMiners by one. Finally, print both values with console.log().

Reference and video

MDN JavaScript variables guide:

https://developer.mozilla.org/en-US/docs/Learn_web_development/Core/Scripting/Variables

Video lesson on var, let, const, and scope:

Next: JavaScript Lesson 2 will build on this foundation with data types, operators, and type checking.