Javascript counter variable not incrementing only appending digits [duplicate]

问题

This question already has answers here:

cannot use + when try to add number (4 answers)

Closed 4 years ago.

  var counter = 0;

  var userAdd = prompt("How many would you like to add?");

  counter += userAdd;

  console.log(counter);

New to javascript.

I am trying to get the counter to increment up by the amount that the userAdd variable specifies.

When I run this code all I get from the console.log() is, for example:

If userAdd is '1' each time:

01
011
0111
...etc.

instead of:

1
2
3

Whats the problem here?

回答1:

You need to type your result as an int rather than a string.

var userAdd = parseInt(prompt("How many would you like to add?"));

This forces the numeric adding instead of the string appending.

来源：https://stackoverflow.com/questions/31061920/javascript-counter-variable-not-incrementing-only-appending-digits