IF statments can be thought of as the fundamental control
statements. It allows the code to be executed IF and only
IF the logic in the expression yields a boolean true value.
The basic syntax for an IF statement:
if (expression)
[{ [code;]+ }] | [code;]
Breaking this down a bit:
expression is any valid boolean-like statement. Since javascript
does not have any real types and all things can be cast into any other
real thing, it is necessary to state what really equates to a boolean
false value.
undefined, null, 0, false
All other things equate to a boolean true statement.
Very simple IF statements that output "It was True".
if (1) document.write("It was True");
if (!0) document.write("It was True");
Note that "!" is "not" - so "not zero" equates to boolean true.
if (1 == 1) document.write("It was True");
Note that "==" is the "is it equals to" condition.
For more complicated compoud expressions:
if (1 == 1 && 0 == 0) document.write("It was True");
Note this reads as: one is equal to one AND zero is equal to zero.
if (1 == 0 || 0 == 0) document.write("It was True");
Note this reads as: one is equal to zero OR zero is equal to zero.
