Referencia de JavaScript 1.5:Sentencias:if...else

De MDC

Tabla de contenidos 1 Summary 2 Syntax 3 Parameters 4 Description 5 Examples 5.1 Example: Using if...else 5.2 Example: Assignment within the conditional expression

[editar] Summary

Executes a statement if a specified condition is true. If the condition is false, another statement can be executed.

Statement
Implemented in:	JavaScript 1.0, NES 2.0
ECMA Version:	ECMA-262

[editar] Syntax

if (condition)
   statement1
[else
   statement2]

[editar] Parameters

condition 

An expression that evaluates to true or false.

statement1 

Statement that is executed if condition evaluates to true. Can be any statement, including further nested if statements. To execute multiple statements, use a block statement ({ ... }) to group those statements.

statement2 

Statement that is executed if condition evaluates to false and the else clause exists. Can be any statement, including block statements and further nested if statements.

[editar] Description

Multiple if...else statements can be nested to create an else if clause:

if (condition1)
   statement1
else if (condition2)
   statement2
else if (condition3)
   statement3
...
else
   statementN

To see how this works, this is how it would look like if the nesting were properly indented:

if (condition1)
   statement1
else
   if (condition2)
      statement2
   else
      if (condition3)
...

To execute multiple statements within a clause, use a block statement ({ ... }) to group those statements. In general, it is a good practice to always use block statements, especially in code involving nested if statements:

if (condition) {
   statements1
} else {
   statements2
}

Do not confuse the primitive boolean values true and false with the true and false values of the Boolean object. Any value that is not undefined, null, 0, NaN, or the empty string (""), and any object, including a Boolean object whose value is false, evaluates to true when passed to a conditional statement. For example:

var b = new Boolean(false);
if (b) // this condition evaluates to true

[editar] Examples

[editar] Example: Using if...else

if (cipher_char == from_char) {
   result = result + to_char;
   x++;
} else
   result = result + clear_char;

[editar] Example: Assignment within the conditional expression

It is advisable to not use simple assignments in a conditional expression, because the assignment can be confused with equality when glancing over the code. For example, do not use the following code:

if (x = y) {
   /* do the right thing */
}

If you need to use an assignment in a conditional expression, a common practice is to put additional parentheses around the assignment. For example:

if ((x = y)) {
   /* do the right thing */
}