Does anyone knows why multiplication of strings works as it were numbers?

Hi there! It's because the plus sign + isn't just an addition symbol. It's also the symbol we use for concatenation. To be clear, this is also true of other programming languages such as Java and C#. JavaScript is pretty smart sometimes and has what it calls "type inference". In many cases, it can deduce the type of data you want by the way you use it.

Take a moment and run this in your console:

let a = "2";
let b = "3";
let c = 4;
let d = 5;

console.log(a + b);
console.log(c + d);
//This is where it gets interesting
console.log(a + c);
console.log(d + b);

// Let's try some other mathematical operations
console.log(a * b);
console.log(b / c);
console.log(a - c);
console.log(c % b);

The output here will be:

• 23
• 9
• 24
• 53
• 6
• 0.75
• -2
• 1

Because a and b are both strings, the + sign means to JavaScript that it should concatenate those two strings and the result will be the string "2" concatenated with the string "3"... or 23. But when we add two numbers together as we did with c + d we get back 9 which is exactly what we'd expect.

It gets interesting when you try and add a number and a string together. This is where JavaScript makes a "best guess". Because you're adding a string with a number, it takes the number and turns it into a string and concatenates it with the other string.

As you can see, all the other mathematical operators work just as expected because it understands that you want a number there. But because the + sign is also used to manipulate strings, it has to make a guess, and it will change it to a string.

In short, if you know you want to do a mathematical operation on numbers, you should always make sure they are numbers first. You can end up with some really unexpected results otherwise.

Hope this clears things up!