Addition is not working in JavaScript

问题:

I am trying to learn Javascript. Here I am confused with the following code.

http://rendera.heroku.com/usercode/eae2b0f40cf503b36ee346f5c511b0e29fc82f9e

When I put x+y in the function it is going wrong. For example 2+2=22, 5+7=57

But /, *, - are working. Why is + not working? Please help me. Thanks a lot in advance

回答1:

One or both of the variables is a string instead of a number. This makes the + do string concatenation.

'2' + 2 === '22';  // true

2 + 2 === 4;  // true

The other arithmetic operators / * - will perform a toNumber conversion on the string(s).

'3' * '5' === 15;  // true

A quick way to convert a string to a number is to use the unary + operator.

+'2' + 2 === 4;  // true

...or with your variables:

+x + +y

回答2:

+ has two uses. One is addition, the other however is string concatenation. If one or both of your variables is a string, then + will concatenate them.

You will need to use parseInt or parseFloat to turn a string into a number.

回答3:

In Javascript the + operator can either perform addition or concatenation depending on the type of its operands. When numbers are used with + it uses addition, but when strings are used with + it concatenates (joins the strings) instead

回答4:

If the numbers that you are trying to add are 10 and 12, if they resulting sum is supposed to be 22, then you should probably do it as

+10 + +12

And the result might be a string like 1012 if one or both of the numbers is a string.

回答5:

this works every time

((x*1) + (y*1))

回答6:

Unary plus should work:

var totalVal = (+2) + (+2);

alert(totalVal);
// result 4

回答7:

The addition operator works the following way:
1) If at least one operand is a string, then another is converted to string and concatenation is performed;

1 + "2"        // "12"
"2" + "3"      // "23"
"2" + null     // "2null", null is converted to "null"

2) In other cases both operands are converted to numbers:

1 + null      // 2, null is converted to 0
1 + undefined // NaN, undefined is converted to NaN

Check the post JavaScript's addition operator demystified for more details.