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JavaScript determines whether a variable is a numeric instance

Source: Internet
Author: User
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Using isNaN () to determine the number

The isNaN () function checks whether its arguments are non-numeric values.

Description

The isNaN () function can be used to determine whether its argument is NaN, which represents an illegal number (such as the result of being 0 apart).

If the result of Nan being compared to any value (including itself) is false, you cannot use the = = or = = operator to determine whether a value is NaN. Because of this, the isNaN () function is required.


Test:

The code is as follows Copy Code


document.write (isNaN (123)); False
document.write (isNaN (-1.23)); False
document.write (isNaN (5-2)); False
document.write (isNaN (0)); False
document.write (isNaN ("Hello")); True
document.write (isNaN ("2005/12/12")); True
document.write (isNaN ("6/2")); True
document.write (isNaN ("3")); False


Cases

Calculates the parameter, and returns True if the value is NaN (not a number). This function can be used to check whether a mathematical expression was successfully evaluated as a number.

The code is as follows Copy Code

if (isNaN (Document.login.imgcode.value)) {
Alert (' Authentication code must be a number! ')
Document.login.imgcode.focus ();
return false;
}

if (!isnum (document.getElementById ("Prjsum"). Value) {
Alert ("Cost can only be a number");
document.getElementById ("Prjsum"). focus ();
return false;

}


use regular expressions to check numbers

It's a good one. The code that is used to check whether the character entered is a number is not a common way of writing.

The code is as follows Copy Code
<! DOCTYPE HTML PUBLIC "-//w3c//dtd HTML 4.01//en" "HTTP://WWW.W3.ORG/TR/HTML4/STRICT.DTD" >
<meta http-equiv= "Content-type" content= "text/html; charset=gb2312 "/>
<title>untitled document</title>
<body>
<input type= "text" id= "Myinput" value= ""/>
<input type= "button" value= "OK" id= "MyButton"/>
</body>
<script language= "JavaScript" type= "Text/javascript" >
function $ (obj) {
return Document.getelementbyidx (obj);
}
function Checkisinteger (str)
{
If empty, the checksum is passed
if (str = "")
return true;
If/^ (-?) (d+) $/.test (str))
return true;
Else
return false;
}
String.prototype.trim = function ()
{
Return This.replace (/(^[s]*) | ( [s]*$)/g, "");
}
$ ("MyButton"). Onclick=function () {

if (Checkisinteger ($ ("Myinput"). Value.trim ())) {
Alert ("Success");
}else{
Alert ("Only a number");
}
}
</script>

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