JAVASCRIPT

jquery validation on button click

$('#btn').on('click', function() {
    $("#form1").valid();
});

jquery validation on click

//html code
<input type="text" id="firstname">
<button onclick="myfunction()">click me</button>

//javascript function
myfunction(){
	//get value of element
	if(document.getElementById('firstname').value==''){
		alert() // if firstname is null, alert will popup.
	}
}