Why is the last operation returning 20?
console.log(2 + 2); // equals 4
console.log("2" + "2"); // equals "22"
console.log(2 + 2 - 2); // equals 2
console.log("2" + "2" - "2"); // equals 20
Asked
Active
Viewed 76 times
2
-
Infact doing ```"2"+"2"-"2"+"2"``` returns "202" this is intresting – Nishant S Vispute May 17 '21 at 05:45
-
Because 22 - 2. Note that strings do not have a `-` operator so the `"22"` is coerced into a number `22` – slebetman May 17 '21 at 05:45
-
2Please don't upload [images of code](https://meta.stackoverflow.com/a/285557/3082296). They can't be copied to reproduce the issue, they aren't searchable for future readers and they are harder to read than text. Please post the actual code **as text** to create a [mcve]. – adiga May 17 '21 at 05:45
-
@NishantShamVispute `"2"+"2"-"2"+"2"` -> `"22" - "2" + "2"` -> `20 + "2"` -> `"202"` – adiga May 17 '21 at 05:47
-
@VLAZ there must be a couple of questions with chaining them together somewhere. – adiga May 17 '21 at 05:50
-
@adiga probably. Can't think of one off the top of my head but it might be under the type coercion rather than just `+` and `-`. I'll try to have a look when I have the time. – VLAZ May 17 '21 at 05:52
-
@adiga yeah i now get the concepts of **concatenation** & **coerce** – Nishant S Vispute May 17 '21 at 05:59
2 Answers
11
+ and - evaluate left-to-right. When either operand is a string, the result is concatenation. When both are numbers, the result is addition.
In contrast, - will always coerce both sides to numbers.
'2' + '2' - '2'
does
// left-to-right
('2' + '2') - '2'
// both sides are strings, so concatenate
'22' - '2'
// operator is -, so coerce both sides to numbers
22 - 2
20
CertainPerformance
- 356,069
- 52
- 309
- 320
1
The signs + and - work very differently in string concatenation. The + operator gives direct concatenation instructions on strings whereas the - operator tries to coerce the types and perform the mathematical function.
console.log("2" + "2");
console.log(typeof ("2" + "2"));
console.log("2" - "2");
console.log(typeof("2" - "2"));
Charlie
- 22,886
- 11
- 59
- 90
-
"*The + operator gives direct concatenation instructions on strings whereas the - operator tries to coerce the types and perform the mathematical function.*" The `+` operator will also do coercion when mixed type operands are used. Which is what happens with `s1 - s2 + s3` if all three are strings containing valid numerics. `s1 - s2` would produce a number, and `+ s3` would coerce back to string. – VLAZ May 17 '21 at 07:44
-
`+` operator will try to perform the concatenation by coercing if non-string values are given. – Charlie May 17 '21 at 08:31
-
-