how to multiply all values of integers in js code example

Example 1: javascript how to multiply numbers

<!-- Multiplying two numbers in HTML and Javascript -->

<main>
<label for="firstNum">Number 1:</label>
<input type="number" id="firstNum" name="firstNum">

<label for="secondNum">Number 2:</label>
<input type="number" id="secondNum" name="secondNum"></br></br>

<button onclick="multiply()">Multiply</button></br></br>

<label for="result">Result</label>
<input type="number" id="result" name="result"/>
</main>

<script>
function multiply(){
	num1 = document.getElementById("firstNum").value;
	num2 = document.getElementById("secondNum").value;
	result = num1 * num2;
	document.getElementById("result").value = result;
}
</script>

Example 2: multiply all numbers in an array javascript

The cause is already known. Here's an alternative - using Array.reduce for your method:

console.log( [1, 2, 3].reduce( (a, b) => a * b ) );
console.log( Array.from( {length: 20} )
  .map( (v, i) => i + 1 )
  .reduce( (a,b) => a * b )
  .toLocaleString());

// for empty arrays, use some initial value
const arr = [];
if (arr.reduce( (a, b) => a * b, -1 ) === -1) {
  console.error(`The given array ${arr} is empty`);
}