Javascript long integer

Question

I have seen one of the weirdest things in javascript. The server side (spring):

   @RequestMapping(value = "/foo", method = RequestMethod.GET)    @ResponseBody    public Long foo() {       return 793548328091516928L;    } 

I return a single long value and:

$.get('/foo').done(function(data){     console.log(data); }); 

It represents the long integer as "793548328091516900" replacing (rounding indeed) the last two digits with 0s. When i make that GET request from any browser's address bar, the number represented correctly; thus this is a js issue, in my opinion.

Returning a string instead of long from server and handling it with:

var x = new Number(data).toFixed(); 

obviously a solution. But I am not so lucky that, I have to handle a complex POJO (converted to JSON) whose some fields (some are nested) are typed with java.lang.Long type. If i try to cast this POJO to another object does not having fields typed Long, it is obviously cumbersome.

Is there any solution to that obstacle in a clearer way?

Answer 1

In Java, you have 64 bits integers, and that's what you're using.

In JavaScript, all numbers are 64 bits floating point numbers. This means you can't represent in JavaScript all the Java longs. The size of the mantissa is about 53 bits, which means that your number, 793548328091516928, can't be exactly represented as a JavaScript number.

If you really need to deal with such numbers, you have to represent them in another way. This could be a string, or a specific representation like a digit array. Some "big numbers" libraries are available in JavaScript.