Program Structure

Expressions and Statements

An expression is any fragment of code that produces a value: 1 + 2, "hello", myFunc(). A statement is a complete instruction — it does something but doesn't necessarily produce a value. let x = 5; is a statement that contains the expression 5.

Expressions can be nested inside other expressions. Statements are executed sequentially, top to bottom.

Bindings

Bindings (variables) give you a way to hold on to values. let creates a block-scoped binding that can be reassigned. const creates a block-scoped binding that can't be reassigned. var is function-scoped and hoisted — mostly a legacy feature now.

Binding names can include letters, digits, $, and _, but can't start with a digit. A well-chosen name is worth more than a comment.

Control Flow

Programs aren't just straight lines. if/else branches execution based on conditions. while and do loops repeat blocks. for loops provide a compact pattern for counter-based iteration.

break exits a loop immediately. continue skips to the next iteration. Indent consistently — the computer doesn't care, but your future self will.