Programming Tutorials

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switch in Javascript

By: Syed Fazal in Javascript Tutorials on 2008年08月16日 [フレーム]

The cousin of the if statement, the switch statement, allows a developer to provide a series of cases for an expression. The syntax for the switch statement is:

switch ( expression ) {
case value : statement
break ;
case value : statement
break ;
case value : statement
break ;
...
case value : statement
break ;

}

Each case says “if expression is equal to value , execute statement ”. The break keyword causes code execution to jump out of the switch statement. Without the break keyword, code execution falls through the original case into the following one.

The default keyword indicates what is to be done if the expression does not evaluate to one of the cases (in effect, it is an else statement). Essentially, the switch statement prevents a developer from having to write something like this:

if (i == 25)
alert(“25”);
else if (i == 35)
alert(“35”);
else if (i == 45)
alert(“45”);
else
alert(“Other”);

The equivalent switch statement is:

switch (i) {
case 25: alert(“25”);
break;
case 35: alert(“35”);
break;
case 45: alert(“45”);
break;
default: alert(“Other”);
}

Two big differences exist between the switch statement in JavaScript and Java. In Javascript, the switch statement can be used on strings, and it can indicate case by nonconstant values:

var BLUE = “blue”, RED = “red”, GREEN = “green”;

switch (sColor) {
case BLUE: alert(“Blue”);
break;
case RED: alert(“Red”);
break;
case GREEN: alert(“Green”);
break;
default: alert(“Other”);
}

Here, the switch statement is used on the string sColor , whereas the case s are indicated by using the variables BLUE , RED , and GREEN , which is completely valid in JavaScript.

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