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:
this works every time
((x*1) + (y*1))
回答5:
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.
来源：https://stackoverflow.com/questions/8377410/addition-is-not-working-in-javascript