how to increment integer in javascript code example

Example 1: javascript decrement

// Increment
let a = 1;
a++;
++a;
// Decrement
let b = 1;
b--;
--b;

Example 2: how to increment variable value in javascript

var a = 1;
      function increase(){
            var textBox = document.getElementById("text");
            textBox.value = a;
            a++;
      }