stop button click refeshing page

My javascript code seems to work apart from refreshing the field input every time I click the button.
How do I stop this?

I just want to enter in the data and also have the result display the answer in the textbox but I cant see anything as all textboxes go blank when i click the button.

I am just testing so no need to submit the data to php for now.

<script type='text/javascript'>

function formValidator(){
	// Make quick references to our fields
	var firstname = document.getElementById('firstname');
	var age = document.getElementById('age');
	var gend = document.getElementById('gender');
        //  alert("correct");
	// Check each input in the order that it appears in the form!
	if(isAlphabet(firstname, "Please enter only letters for your name")){
			if(isNumeric(age, "Please enter a valid age")){
				if(madeSelection(gend, "Please Choose a Gender")){
							//return true;
	//return false;

function calc()
   // alert("correct");
    var qty1 = document.getElementById("qty").value;
    var amount1 = document.getElementById("amount").value;
    var days;
    var result = 0;

         document.getElementById("total").value =result;

function notEmpty(elem, helperMsg){
	if(elem.value.length == 0){
		elem.focus(); // set the focus to this input
		return false;
	return true;

function isNumeric(elem, helperMsg){
	var numericExpression = /^[0-9]+$/;
		return true;
		return false;

function isAlphanumeric(elem, helperMsg){
	var alphaExp = /^[0-9a-zA-Z]+$/;
		return true;
		return false;

function madeSelection(elem, helperMsg){
	if(elem.value == "Please Choose"){
		return false;
		return true;


First Name: <input type='text' id='firstname' /><br />
Age: <input type='text' id='age' /><br />

Gender: <select id='gender'>
	<option>Please Choose</option>
</select><br />


amount:<input type="text" id="amount" />
Qty<input type="text" id="qty"  />
Result<input type="text" id="total" />
  <button onclick="formValidator()">Check Form</button>  

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Mukesh YadavFull Stack DeveloperCommented:
You need to bind the JavaScript function to the form's onSubmit event handler.

<form onSubmit="javascript:return formValidator();">
<!-- Form fields goes here -->

And in formValidator() function you need a minor modification.
You have to return false when there is an error and true if all data validated successfully.
Brian TaoSenior Business Solutions ConsultantCommented:
2 modifications needed:
- in line#16 you're calling a non-existing function isAlphabet, which I guess is a typo and should be isAlphanumeric
- in line#119 you need to add type="button" to your button tag.

Then you should be good.

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