Check for Valid Date using JavaScript

The following code is helpful to Validate a Date using javascript.

1. Call the Function "OnClientClick" of Button (OnClientClick="ValidateForm())
2. Write the Following Functions in Script tag of Head Section.

Javascript :

    // Declaring valid date character, minimum year and maximum year
    var dtCh= "/";
    var minYear=1900;
    var maxYear=2100;
    
    function isInteger(s)
    {
        var i;
        for (i = 0; i <>
        {
            // Check that current character is number.
            var c = s.charAt(i);
            if (((c < "0") || (c > "9"))) return false;
        }
        // All characters are numbers.
        return true;
    }

    function stripCharsInBag(s, bag)
    {
        var i;
        var returnString = "";
        // Search through string's characters one by one.
        // If character is not in bag, append to returnString.
        for (i = 0; i <>
        {
            var c = s.charAt(i);
            if (bag.indexOf(c) == -1) returnString += c;
        }
        return returnString;
    }

    function daysInFebruary (year)
    {
        // February has 29 days in any year evenly divisible by four,
        // EXCEPT for centurial years which are not also divisible by 400.
        return (((year % 4 == 0) && ( (!(year % 100 == 0)) || (year % 400 == 0))) ? 29 : 28 );
    }
    
    function DaysArray(n)
    {
        for (var i = 1; i <= n; i++)
        {
            this[i] = 31
            if (i==4 || i==6 || i==9 || i==11) {this[i] = 30}
            if (i==2) {this[i] = 29}
        }
        return this
    }

    function isDate(dtStr)
    {
        var daysInMonth = DaysArray(12)
        var pos1=dtStr.indexOf(dtCh)
        var pos2=dtStr.indexOf(dtCh,pos1+1)
        var strMonth=dtStr.substring(0,pos1)
        var strDay=dtStr.substring(pos1+1,pos2)
        var strYear=dtStr.substring(pos2+1)
        strYr=strYear
        if (strDay.charAt(0)=="0" && strDay.length>1)
        strDay=strDay.substring(1)
        if (strMonth.charAt(0)=="0" && strMonth.length>1)
        strMonth=strMonth.substring(1)
        
        for (var i = 1; i <= 3; i++)
        {
            if (strYr.charAt(0)=="0" && strYr.length>1)
            strYr=strYr.substring(1)
        }
        
        month=parseInt(strMonth)
        day=parseInt(strDay)
        year=parseInt(strYr)
        
        if (pos1==-1 || pos2==-1)
        {
            alert("The date format should be : mm/dd/yyyy")
            return false
        }
        if (strMonth.length<1>12)
        {
            alert("Please enter a valid month")
            return false
        }
        if (strDay.length<1>31 || (month==2 && day>daysInFebruary(year)) || day > daysInMonth[month])
        {
            alert("Please enter a valid day")
            return false
        }
        if (strYear.length != 4 || year==0 || yearmaxYear)
        {
            alert("Please enter a valid 4 digit year between "+minYear+" and "+maxYear)
            return false
        }
        if (dtStr.indexOf(dtCh,pos2+1)!=-1 || isInteger(stripCharsInBag(dtStr, dtCh))==false)
        {
            alert("Please enter a valid date")
            return false
        }
        return true
    }

    function ValidateForm()
    {
        var dt;
        dt=document.getElementById('txtDate');
        if (isDate(dt.value)==false)
        {
            dt.focus()
            return false
        }
        return true
    }

Regular Expression for Alphanumeric using Javascript

You can use Javascripts to validate this as followes.

Define the Javascript Function "isNumberEvt" on Head Section. and check it on keypress even of text box like "onkeypress="return isNumberEvt(event)"".

Javascript :

    function isNumberEvt(evt)
    {

        var charCode = (evt.which) ? evt.which : event.keyCode
        if ((charCode > 31 && charCode <> 57 && charCode <> 90 && charCode <> 122))
        return false;

        return true;

    }

aspx:

call function onkeypress="return isNumberEvt(event)" even of Textbox.

    asp:textbox id="TextBox1" onkeypress="return isNumberEvt(event)" runat="server" width="238px"

To Validate Only Digits Using JavaScript

Valdate Textbox to accept only Digits using Javascript.

Use this function on "keyup" event of Textbox.

Javascript:

    function isDigit(evt)
    {
        var charCode = (evt.which) ? evt.which : event.keyCode

        if (charCode > 47 && charCode < 58)
        { 
            return true;
        }
        else
        {   
            return false;
        }      
    }

aspx:

 asp:textbox id="TextBox1" onkeyup="return isDigit(event)" runat="server" width="238px" 

Validate the Maximum no. of Characters allowed in TextBox Using Java Script.

Function for Check and limit the number of characters allowed in a Textbox.

CheckLength(txt,5) : It will allow only 5 Characters in text box.

Javascript :

    function CheckLength(obj,Length)
    {
        if (obj.value.length>Length)
        {
            alert("Exceeding Maximum " + Length +" Characters")
            obj.focus()
            obj.select()
        }
    } 

aspx :

asp:textbox id="TextBox1" onkeyup="CheckLength(this,5)" runat="server" width="238px" 

To Validate Numbers Using JavaScript

Use the following function to Check the object does ahve a Numeric value or not.

javascript :

    function Validatenumber(obj)
    {
        if (obj.length !=0)
        {
            var text = /^[-0-9]+$/;

            if ((document.getElementById(obj.id).value != "") && (!text.test(document.getElementById(obj.id).value)))
            {
                alert("Please enter numeric values only");
                obj.focus();
                obj.select();
            }
        }
    }

For Validating the Year Value Using Javascript ...

The following code used to validate "Year" using javascript.

Javascript :

    function ValidateYear(obj)
    {
        if (obj.length !=0)
        {
            var text = /^[0-9]+$/;

            if ((document.getElementById(obj.id).value != "") && (!text.test(document.getElementById(obj.id).value)))
            {
                alert("Please Enter Numeric Values Only");
                obj.focus();
                obj.select();
            }

            if (document.getElementById(obj.id).value.length>4)
            {
                alert("Year is not proper. Please check");
                obj.focus();
                obj.select();
            }
        }
    }

Reverse the String Using JavaScript

Use the following function to reverse the string using javascript

Example : reverseStr('KnowledgeParlour')

Output    : 'ruolraPegdelwonK'

Javascript :

    function reverseStr(str) 
    {
        if (!str) return; // nothing to change
        var rstr = '';
        for (i=str.length-1;i>=0;i--) 
        {
            rstr += str.charAt(i);
        }
        return rstr;
    }