+$ in jquery. How come not only the basic $

Question

I have some jQuery code where +$(...) is used in many places. The code does not work without the + part, when doing just $(...).

I couldn't find any explanation through Google. I'd appreciate any guidance if possible.

function calculate() {
  var a = +$('#a').val(); // what is +$ ?
  var b = +$('#b').val();
  var c = b * 108.40;
  //etc
}

Answer 1

+$() is actually two operations, where first $() runs to grab your input and then + coerces whatever the value of the input is into a number.

Here's a breakdown of what is happening:

var valueA = $('#a').val(); // "123"
var numberA = +valueA;      //  123

console.log('valueA is a ' + typeof valueA);   // 'valueA is a string'
console.log('numberA is a ' + typeof numberA); // 'numberA is a number'

<script src="https://ajax.googleapis.com/ajax/libs/jquery/2.1.1/jquery.min.js"></script>
<input id="a" value="123"/>