if...else Statement

Conditionally executes a group of statements, depending on the value of an expression.

if (condition)
   statement1
[else 
   statement2] 

Arguments

• condition
  Required. A Boolean expression. If condition is null or undefined, condition is treated as false.

• statement1
  Required. The statement to be executed if condition is true. Can be a compound statement.

• statement2
  Optional. The statement to be executed if condition is false. Can be a compound statement.

Remarks

It is generally good practice to enclose statement1 and statement2 in braces ({}) for clarity and to avoid inadvertent errors.

Example

In the following example, you may intend that the else be used with the first if statement, but it is used with the second one.

var z = 3;
if (x == 5)
    if (y == 6)
        z = 17;
else
     z = 20;

The above example is equivalent to the following code:

var z = 3;
if (x == 5)
    {
    if (y == 6)
        z = 17;
    else
        z = 20;
    }

Changing the code in the following manner eliminates any ambiguities:

if (x == 5)
    {
    if (y == 6)
        z = 17;
    }
else
    z = 20;

Similarly, if you want to add a statement to statement1, and you do not use braces, you can accidentally create an error:

if (x == 5)
    z = 7;
    q = 42;
else
    z = 19;

In this case, there is a syntax error, because there is more than one statement between the if and else statements. Braces are required around the statements between if and else.

Requirements

Version 1

See Also

Reference

Conditional (Ternary) Operator (?:)

Change History

Date	History	Reason
March 2009	Clarified first example.	Information enhancement.