interview_use.js

// For Javascript I use (commonJS) 

const swapNumber = (a, b) => {
  let temp = a;
  
  a = b;
  b = temp;
  
  
  return [a, b];
}; 

// Execution:

const  num1 = 20;
const num2 = 30;

[num1, num2] = swapNumber(num1, num2);

console.log(num1);
console.log(num2);

// ----------


// My ans for php 


function swapNumber($a, $b) {
    $temp = $a;
    $a = $b;
    $b = $temp;
  
  
    return array($a, $b);
}

// Call func

$a = 20;
$b = 30;

list($firstNum, $secondNum) = swapNumber($firstNum, $secondNum);

echo $firstNum."\n";
echo $secondNum;

No worries, after the interview , this gist will be deleted.