Your First JavaScript Program

A JavaScript program is made from statements and expressions. An expression produces a value; a statement performs an action or controls the flow of execution. Semicolons are often optional because JavaScript has automatic semicolon insertion, but consistent style makes code easier to read.

const name = "Asha";
const completedLessons = 3;
const totalLessons = 10;

console.log(`Welcome, ${name}!`);
console.log(`Progress: ${completedLessons}/${totalLessons}`);

The const declarations create bindings that cannot be reassigned. Template literals use backticks and ${...} to insert evaluated expressions into a string.

Comments#

// A single-line comment

/*
  A multi-line comment can explain
  a non-obvious decision.
*/

Prefer meaningful names and code that explains itself. Comments are most useful for intent, constraints, and reasons that are not obvious from the code.

Values and output#

console.log can display strings, numbers, booleans, arrays, and objects. You can log several values at once:

const price = 250;
const quantity = 2;
console.log("Total:", price * quantity);

Common beginner mistakes#

• Misspelling a variable name; identifiers are case-sensitive.
• Using a variable before it has been initialized.
• Expecting "5" + 1 to behave like 5 + 1 without understanding coercion.
• Forgetting which environment a browser-only API belongs to.

Practice#

Create a program that stores your name, the course name, and the number of lessons you want to finish this week, then logs a short summary.