How to validate required field in a form using javascript

How to validate required field in a form using javascript

In a wave form, fields are needs to validate at the time of entry or on submission of form. Generally in a form it needs to validate user has left required fields empty or not, user has entered valid e-mail address or not, user has entered a valid date, user has entered text in a numeric field or not and other also. 

Here is a function below to validate if a required field has been left empty. If the required field is blank, an alert box alerts a message and the function returns false. If a value is entered, the function returns true.


 Function to validate required field in a form using javascript


function validate_required(field, alerttxt)
{
with (field)
{
if (value==null||value=="")
	{alert(alerttxt); return false}
else {return true}
}
}

Full script, with the HTML form to validate required field 









Email:






Preview of the above code, to validate required field 






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