JavaScript中的'2'+'2' - '2'= 20怎么样？

Question

I was just randomly playing around JavaScript. The '2'+'2'-'2' input I given to it.

and the output is surprisingly 20 .

 console.log('2'+'2'-'2'); 

Now I am not getting it.

Does anyone explain is to me Why it is like this? How can be output of this equal to 20 ?

Answer 1

+ is both concatenation and addition. If any of the arguments are not numeric, then it's concatenation. Thus, '2' + '2' is '22' - just like "foo" + "bar" are "foobar" , and just like 3 + {} is "3[object Object]" .

- is only subtraction. No matter what its arguments are, they are coerced to numbers. Thus, '22' - '2' is evaluated as 22 - 2 , which is 20.

Answer 2

JavaScript performs string concatenation when find + . So the first "2" and second "2" makes "22".

But when performing subtraction ( - ) on strings, coercion happens. So the resulted "22" coerced to number 22 and final "2" coerced to number 2 . Finally subtracts 2 from 22 to result 20 .

For More: Coercion

Step by step evaluation:

'2' + '2' - '2' To

'22' - '2' To

22 - 2 To 20

Answer 3

The mechanism at play in JavaScript is called coercion .

The + sign in JavaScript can either perform string concatenation, or arithmetic addition. So how does JavaScript choose which action to perform?

In case both arguments (on either side of the +) are strings, JavaScript performs a concatenation.

 console.log(2 + 2); // 4 console.log('2' + '2'); // '22' 

The minus sign however has only one meaning: the arithmetic subtraction.

So JavaScript has only one way to interpret '22' - 2 which is to subtract 2 from '22'. But of course '22' is not a number, so JavaScript first forces it ("coerces" it) into a number.

The real operation performed is 22 - 2 , which easily computes to 20 , the result you observe.