IF

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Javascript Reserved Word – IF

IF statements 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 compound 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.

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