I’ve highlighted here only those elements of JavaScript syntax that someone familiar with other languages (especially C-like languages) might want to know.

JavaScript line comments are demarcated by the // symbol. Block comments are formed using /* and */.

Statements are semicolon-terminated. It’s wise to forget about so-called optional semicolons and semicolon insertion by the interpreter.

Strings can be either single or double-quoted.

Variables are declared with var, or more recently, with let and const. var has function scope, or else global scope; let and const have block scope only.

Booleans are true and false.

undefined is the value assigned to a name to which no other value has yet been assigned. null is a value standing for no value.