将 +1 添加到只读文本输入字段的 jQuery 值

Question

I am using a function where I have a readonly text input , and when I execute the function I want the number value + 1. So let's say I have 60, when I execute the function, the number returned should be 61.

But instead it's coming out 601, which is just adding the number 1 to the string. Any clue as to what is going on? Subtraction, multiplication and division all work fine. Here is a snippet

 var num= $("#originalnum").val() + 1;
 $("#originalnum").val(num);

And yes i've tried a few different variations, am I missing something?

Answer 1

A simple unary + is sufficient to turn a string into a number in this case:

var num = +$("#originalnum").val() + 1;
$("#originalnum").val(num);

Answer 2

The problem is that .val() returns the value of the element as a string, and when you use the + operator on a string it does string concatenation. You need to convert the value to a number first:

var num = +$("#originalnum").val() + 1;            // unary plus operator
// OR
var num = Number($("#originalnum").val()) + 1;     // Number()
// OR
var num= parseFloat($("#originalnum").val()) + 1;  // parseFloat()
// OR
var num= parseInt($("#originalnum").val(),10) + 1; // parseInt()

Note that if you use parseInt() you must include the radix (10) as the second parameter or it will (depending on the browser) treat strings with a leading zero as octal and strings with a leading "0x" as hexadecimal. Note also that parseInt() ignores any non-numeric characters at the end of the string, including a full-stop that the user might have intended as a decimal point, so parseInt("123.45aasdf",10) returns 123 . Similarly parseFloat() ignores non-numeric characters at the end of the string.

Also if it's a user-entered value you should double-check that it actually is a number and perhaps provide an error message if it isn't.

When you use the * , / or - operators JS tries to convert the string to a number automatically, so that's why those operators "work" (assuming the string can be converted).

Answer 3

You should use the parseInt function and make sure the value is number(use isNaN function):

var val = $("#originalnum").val();

var num = 0;

if ( !isNaN(val) )
  num= parseInt(val) + 1;

Answer 4

Use parseInt() :

var num= parseInt($("#originalnum").val(),10) + 1;

So your number is treated as an integer instead of a string (as .val() treats the result as string by default)

Answer 5

If you don't like the above code spelling, you can try it this way too.

$("#originalnum").val(function() {
   $(this).val(parseInt($(this).val()) + 1)
});