learned in Chapter 4, an
expression is a combination of values, variables, operators, and functions
that results in a value; the result can be a number, a string, or a
Boolean value (which evaluates to either
Example 14-1 shows some
simple expressions. For each line, it prints out a letter between
followed by a colon and the result of the expressions (the
<br /> tag is there to create a line break
and separate the output into four lines).
<script> document.write("a: " + (42 > 3) + "<br />") document.write("b: " + (91 < 4) + "<br />") document.write("c: " + (8 == 2) + "<br />") document.write("d: " + (4 < 17) + "<br />") </script>
The output from this code is as follows:
a: true b: false c: false d: true
Notice that expressions
d: evaluate to
c: evaluate to
false. Unlike PHP (which would print the number
“true” and “false”.
false, all values evaluate to
true with the exception of the following, which
false: the string
NaN (Not a Number, a
computer engineering concept for an illegal floating-point operation such
as division by zero).
Note that I am referring to
false in lowercase. This is because, unlike in PHP, these ...