Type coercion in arithmetic operations in JavaScript

The + operator is special

+ means two different things depending on what's around it:

• If either side is a string → it joins them together (concatenation)
• If both sides are numbers → it adds them

console.log("1" + 1); 
// "1" is a string, so JS turns the whole thing into string joining
// "1" + "1" → "11"

console.log(1 + "1"); 
// Same thing, order doesn't matter - one side is a string
// "1" + "1" → "11"

console.log(1 + 1); 
// Both are actual numbers, so this is real math
// → 2

Think of it like glueing vs adding. If either piece is text, JS assumes you want to glue them together like sentences.

console.log("Hello" + " " + "World"); 
// All strings, so they just get glued end to end
// "Hello" + " " → "Hello "
// "Hello " + "World" → "Hello World"

The other operators (-, *, /, %) are NOT special

These operators only make sense for numbers — there’s no such thing as “subtracting” or “multiplying” text. So JavaScript always tries to convert strings to numbers first, no matter what.

console.log("5" - 2); 
// "5" gets converted to the number 5
// 5 - 2 → 3

console.log("5" * 2); 
// "5" becomes 5
// 5 * 2 → 10

console.log("5" / 2); 
// "5" becomes 5
// 5 / 2 → 2.5

console.log("5" % 2); 
// "5" becomes 5
// 5 % 2 (remainder of 5 divided by 2) → 1

Easy rule to remember

OperatorIf a string is involved+Glues strings together (or numbers, if both are strings)-, *, /, %Converts string to number, then does math

A fun trick people use to convert a string to a number is:

console.log("5" - 0); 
// 5 (as a number now, not a string)

Because - forces numeric conversion, subtracting 0 doesn't change the value but turns it into a real number.