JavaScript 2.0-The Complete Reference, Second ... - freecodingtutorial

The last operator that is associated with objects is the parentheses operator. This operator is
used to invoke an object‘s method just as it invokes functions. For example, we have already
seen the Document object‘s write() method:
document.write("Hello from JavaScript");
In this case, we pass a single parameter, the string "Hello from JavaScript", to the write method
so that it is printed to the HTML document. In general, we can invoke arbitrary object methods
as follows:
objectname.methodname(optional parameters)
Operator Precedence and Associativity
Operators have a predefined order of precedence, that is, order in which they are evaluated in
an expression. This is particularly obvious with arithmetic operators and is similar to the
evaluation of equations in algebra, where multiplication and division have higher precedence
over addition and subtraction. For example, the result of
alert(2 + 3 * 2);
will be 8 because the multiplication is performed before the addition. We see that multiplication
has higher precedence than addition. Using parentheses, we can group expressions and force
their evaluation in an order of our choice. Parenthesized expressions are evaluated first. For
example,
alert((2 + 3) * 2);
will display 10.
Of course, expression evaluation is also influenced by the operator associativity. Associativity
essentially means the ―direction‖ in which an expression containing an operator is evaluated.
For example, consider the following combination of addition and string concatenation
operations:
alert(5 + 6 + "Hello");
The result will be the string "11Hello" rather than "56Hello." Even though the two instances of +
would appear to have the same precedence, the + operator is ―left associative,‖ meaning that it
is evaluated left to right, so the numeric addition is performed first. Conversely, in this example,
var y;
var x = y = 10 * 10;
the multiplication is performed first because assignment (=) is ―right associative.‖ The result is
that 100 is computed, then assigned to y, and only then assigned to x.
The precedence and associativity of the various operators in JavaScript is presented in Table
4-9. Note that by computer science tradition, precedence is indicated by a number, with lower
numbers indicating higher precedence.