Name
&& — NN 2 IE J1 ECMA 1
Synopsis
The AND operator. This operator compares two Boolean expressions for
equality. If both expressions evaluate to true
,
the result of the &&
operator also
evaluates to true
; if either or both expressions
are false
, the &&
operator evaluates to false
.
A Boolean expression may consist of a comparison expression (using any of the many comparison operators) or a variety of other values. Here are the most common data types, values, and their Boolean value equivalent.:
Data Type |
Boolean Equivalent |
---|---|
Number other than zero |
true |
Zero |
false |
Any nonempty string |
true |
Empty string |
false |
Any object |
true |
|
false |
|
false |
Using this information, you can create compound conditions with the
help of the &&
operator. For example, if
you want to see if someone entered a value into a form field and it
is a number greater than 100, the condition would look like the
following:
var userEntry = document.forms[0].entry.value if (userEntry && parseInt(userEntry) >= 100) { ... }
If the user had not entered any value, the string is an empty string.
In the compound condition, when the first operand evaluates to
false
, the &&
operator
rules mean that the entire expression returns
false
(because both operands must be
true
for the operator to return
true
). Because evaluation of expressions such as
the compound condition are evaluated from left to right, the
false
value of the first operand short-circuits
the condition to return false
, meaning that the second ...
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