Operatori in JavaScript

P	A	Operator	Operand type(s)	Operation performed
15	L	.	object, identifier	Property access
	L	[]	array, integer	Array index
	L	( )	function, arguments	Function call
	R	new	constructor call	Create new object
14	R	++	lvalue	Pre- or post-increment (unary)
	R	--	lvalue	Pre- or post-decrement (unary)
	R	-	number	Unary minus (negation)
	R	+	number	Unary plus (no-op)
	R	~	integer	Bitwise complement (unary)
	R	!	boolean	Logical complement (unary)
	R	delete	lvalue	Undefine a property (unary)
	R	typeof	any	Return data type (unary)
	R	void	any	Return undefined value (unary)
13	L	*, /, %	numbers	Multiplication, division, remainder
12	L	+, -	numbers	Addition, subtraction
	L	+	strings	String concatenation
11	L	<<	integers	Left shift
	L	>>	integers	Right shift with sign-extension
	L	>>>	integers	Right shift with zero extension
10	L	<, <=	numbers or strings	Less than, less than or equal
	L	>, >=	numbers or strings	Greater than, greater than or equal
	L	instanceof	object, constructor	Check object type
	L	in	string, object	Check whether property exists
9	L	==	any	Test for equality
	L	!=	any	Test for inequality
	L	===	any	Test for identity
	L	!==	any	Test for non-identity
8	L	&	integers	Bitwise AND
7	L	^	integers	Bitwise XOR
6	L	|	integers	Bitwise OR
5	L	&&	booleans	Logical AND
4	L	||	booleans	Logical OR
3	R	?:	boolean, any, any	Conditional operator (3 operands)
2	R	=	lvalue, any	Assignment
	R	*=, /=, %=, +=, -=, <<=, >>=, >>>=, &=, ^=, |=	lvalue, any	Assignment with operation
1	L	,	any	Multiple evaluation

The column labeled "P" specifies the precedence of each operator. Operator precedence controls the order in which operations are performed. Operators with higher numbers in the "P" column are performed before those with lower numbers.
Consider the following expression:

w = x + y*z; 

The multiplication operator * has a higher precedence than the addition operator +, so the multiplication is performed before the addition. Furthermore, the assignment operator = has the lowest precedence, so the assignment is performed after all the operations on the righthand side are completed.

Obs.

• In JavaScript all numbers are floating-point, so all divisions have floating-point results: 5/2 evaluates to 2.5, not 2. 
• While the modulo operator is typically used with integer operands, it also works for floating-point values. For example, -4.3 % 2.1 evaluates to -0.1. 

http://docstore.mik.ua/orelly/webprog/jscript/ch05_02.htm