How to convert the expression PS I am writing a calculator???

U

Umid2015-10-11 01:07:40

JavaScript

Umid, 2015-10-11 01:07:40

Hello!
I am writing a calculator in js, and the first problem arose.
The code:

<!DOCTYPE html>
<html lang="en">
<head>
  <meta charset="UTF-8">
  <title>JavaScript</title>
  <script src="jsLessons.js"></script>
</head>
<body>
  <input type="text" id="text" onchange="calcFunc(this.value)">
  <input type="button" value="Кнопка" id="button">
</body>
</html>

function calcFunc(newS){
  alert(parseInt(newS));
}

And when writing in the script in place of parseInt - Number(newS) - gives out NaN for the expression 53+65 (for example)
And when parseInt it gives out only the first number - for example for the expression 53+65 - it gives out only 53.
How can I convert from String to numeric value, the whole expression??