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Creating a conversion function

A conversion function is relatively simple: You need two arguments, one for the value to be converted

and one indicating what type of conversion should take place. Generally speaking, three conversions are

frequently used: convert to integer, convert to float, and convert to date. Of course, if you need a string,

no conversion is necessary.

For this conversion function, the second argument is a string indicating the type of conversion to do:

“int” to convert to an integer

“float” to convert to a float

“date” to convert to a date

Any other value always returns a string

Here’s the function:

function convert(sValue, sDataType) {

switch(sDataType) {

case “int”:

return parseInt(sValue);

case “float”:

return parseFloat(sValue);

case “date”:

return new Date(Date.parse(sValue));

default:

return sValue.toString();

}

This function uses the

switch

statement to determine the value of

sDataType

(remember, the

switch

statement works on all types in JavaScript). When

sDataType

“int”

parseInt()

is called on

sValue

and the result is returned; when

sDataType

“float”

parseFloat()

is called and the result

is returned. If

sDataType

“date”

, then

Date.parse()

is used in conjunction with the

Date

construc-

tor to create and return a new

Date

object. If

sDataType

is any other value, the function returns

sValue.toString()

, to ensure that a string value is returned. This means that if

sDataType

“string”

null

, or any other value,

convert()

always returns a string. For example:

var sValue = “25”;

var iValue = convert(sValue, “int”);

alert(typeof iValue); //outputs “number”

var sValue2 = convert(sValue, “string”);

alert(typeof sValue2); //outputs “string”

var sValue3 = convert(sValue);

alert(typeof sValue3); //outputs “string”

var sValue4 = convert(sValue, “football”);

alert(typeof sValue4); //outputs “string”

In this example,

convert()

is used to convert the string

“25”

into an integer, meaning that when

typeof

is called against it, the value returned is

“number”

. If, however, the second argument is

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Chapter 12

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