How to restrict an input field to a numeric input field using JavaScript

numeric-input.js

/*
 * Avoid the A-Z a-z and special characters in text boxes
 */
jQuery(document).on('keypress', 'input.numeric', function(e) {
	
	/* avoid entering multiple '.' */
	if (e.currentTarget.value)
	{
		var keyCode = e.which ? e.which : e.keyCode;
		var c = String.fromCharCode(keyCode);
		
		/* fix DEL key for FF */
		if (e.which == '0')
		{
			return true;
		}
		
		/* for avoid multiple '.' */
		else if (c === '.' && e.currentTarget.value.indexOf('.') > -1)
		{
			return false;
		}
		/* disable space bar */
		else if (keyCode === 32){
			return false;
		}
		
	}
	
	if (navigator.appName == "Opera") 
	{
		var c = String.fromCharCode(e.keyCode);
		if (/[\%\_']/.test(c))return false;
		else if ((e.keyCode == 37)// left
			|| (e.keyCode == 8)// backspace
			|| (e.keyCode == 9)// tab
			|| (e.keyCode == 39)// right
		)return true;
		else if (/[ \d\.]/.test(c))return true;
		else return false;
	}
	else if (navigator.appName == "Netscape") 
	{
		var c = String.fromCharCode(e.charCode);
		if (/[\%\_']/.test(c))return false;
		else if ((e.keyCode == 37)// left
				|| (e.keyCode == 8)// backspace
				|| (e.keyCode == 9)// tab
				|| (e.keyCode == 39)// right
				|| (e.keyCode == 46)// DEL
			)return true;
		else if (/[ \d\.]{1,}$/.test(c))return true;
		else return false;
	}
	else if (/Microsoft/.test(navigator.appName)) 
	{
		var c = String.fromCharCode(e.keyCode);
		if (/[\%\_']/.test(c))return false;
		else if ((e.keyCode == 37)// left
				|| (e.keyCode == 8)// backspace
				|| (e.keyCode == 9)// tab
				|| (e.keyCode == 39)// right
			)return true;
		else if (/[ \d\.]/.test(c))return true;
		else return false;
	}
	else 
	{
		var CharKey = (e.keyCode) ? e.keyCode : e.charCode;
		var c = String.fromCharCode(CharKey);
		if (/[\%\_']/.test(c))return false;
		else if ((e.keyCode == 37)// left
				|| (e.keyCode == 8)// backspace
				|| (e.keyCode == 9)// tab
				|| (e.keyCode == 39)// right
			)return true;
		else if (/[ \d\.]/.test(c))return true;
		else return false;
	}
	
});