The correct syntax for an if statement in JavaScript is if (condition) { code }. The condition must be enclosed in parentheses, and the code to be executed if the condition is true is enclosed in curly braces. If the code block has only one statement, the curly braces can be omitted, but it's generally considered good practice to include them for better readability and to prevent errors when adding more statements later. Unlike some other languages, JavaScript does not use keywords like 'then' in its if statements.