AJAX - The Complete Reference

PART IV

Appendix A: JavaScript Quick Reference 571

Logical Operators

Logical operators operate upon Boolean values and are used to construct conditional

statements. Logical operators are short-circuited in JavaScript, meaning that once a logical

condition is guaranteed, none of the other subexpressions in a conditional expression are

evaluated. They are evaluated left to right. Table A-15 summarizes these operators.

Conditional Operator

The conditional operator is a ternary operator popular among C programmers. Its syntax is

( expr1? expr2 : expr3 )

where expr1 is an expression evaluating to a Boolean and expr2 and expr3 are expressions. If

expr1 evaluates true then the expression takes on the value expr2; otherwise, it takes on the

value expr3. The operator has gained some popularity in JavaScript, serving as a compact

simple conditional often used in feature detection.

var allObject = (document.all)? true : false;

Type Operators

Type operators generally operate on objects or object properties. The most commonly used

operators are new and typeof, but JavaScript supports a range of other type operators as

well, summarized in Table A-16.

Operator Example

>>>= var x = 4;

x >>>= 2;

//1

&= var x = 4;

x &= 5;

//4

|= var x = 4;

x |= 2;

//6

^= var x = 5;

x ^= 3;

//6

TABLE A-14 Binary and Self-Assignment Bitwise Operators (continued)

Operator Description Example

&& Logical AND true && false // false

|| Logical OR true || false // true

! Logical negation! true // false

TABLE A-15 Logical Operators