JavaScript Switch Case

You can use multiple if… else if statement, as in the previous chapter, to perform a multi-way branch. However, this is not always the best solution, especially when all of the branches depend on the value of a single variable.

Starting with JavaScript 1.2, you can use a SWITCH statement that handles exactly this situation, and it does so more efficiently than repeated if..else if statements.  

Syntax 

The basic syntax of the switch statement is to give expression to evaluate and several different statements to execute based on the value of the expression. The interpreter checks each case against the value of the expression until a match is found, if nothing matches, a default condition will be used.  

Switch(expression)

{ case condition 1 : statement(s) break;

Case condition 2: statement(s) break;

… Case condition n: statement(s) break;

default: statement(s)

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break 

statements indicate to the interpreter the end of that particular case. If they were omitted, the interpreter would continue executing each statement in each of the following cases We will explain the break statements in the LOOP Control chapter.  

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Example Following example illustrates a basic while loop:

<script type=”text/javascript”>

<!— var grade=’A’; document.write(“Entering switch block <br/>”);

switch(grade) { case ‘A’ : document.write(“Good job<br />”);

break; Case ‘B’ :doucument.write(“Pretty good <br/>”);

break; case ‘C’: document.write(“Passed<br />”);

break; Case ‘D’ :document.write(“Not So good <br/>”);

break; Case ‘F’ :documenet.write(“Failed <br/>”);

break; default :document.write(“Unknown grade<br/>”) break;

} document.write(“Existing switch block”); //-- >

</script>

  Example

Consider a case if you do not use break statement:

<script type=”text/javascript”>

<!— var grade=’A’; document.write(“Entering switch block<br/>”);

switch(grade) { Case ‘A’ :document.write(“Good job <br />”);

Case ‘B’ :document.write(“Pretty good <br />”);

Case ‘C’ :document.write(“Passed<br/>”);

Case ‘D’ :document.write(“Not So good <br />”);

Case ‘F’ :document.write(“Failed <br />”);

default: document.write(“Unknown grade<br/>”); }

document.write(“Existing switch block”); //-- >

</script>