Post-increment operator does not increment variable until after evaluation [duplicate]

Answer 1

Because you use the postfix increment operator variable++, that means you get the value first and then the variable is incremented.

When you use prefix increment operator ++variable, the variable gets incremented first and then the value is returned.

var a = 42;
console.log(a++); // shows 42, value is 43
console.log(a);   // 43
console.log(++a); // 44
console.log(a);   // 44

Answer 2

Instead of using a++ you can do ++a to get the increment before the variable value assignation:

var a = 14;
document.getElementById("php").innerHTML = ++a;

<div id="php"></div>

Answer 3

It does increase the variable, however it writes to the innerHTML then increments the value, You could use ++a which will increase the value before it writes to the innerHTML.

var a = 14
var b = 14
console.log('before a', a)
document.getElementById("test1").innerHTML = a++
console.log('after a', a)

console.log('before b', b)
document.getElementById("test2").innerHTML = ++b
console.log('after b', b)

<div id="test1"></div>
<div id="test2"></div>