Determine if JavaScript value is an "integer"? [duplicate]

Question

Possible Duplicate:
Check if a variable contains a numerical value in Javascript?

How do I check if variable is an integer in jQuery?

Example:

if (id == int) { // Do this } 

Im using the following to get the ID from the URL.

var id = $.getURLParam("id"); 

But I want to check if the variable is an integer.

Answer 1

Try this:

if(Math.floor(id) == id && $.isNumeric(id))    alert('yes its an int!'); 

$.isNumeric(id) checks whether it's numeric or not
Math.floor(id) == id will then determine if it's really in integer value and not a float. If it's a float parsing it to int will give a different result than the original value. If it's int both will be the same.

Answer 2

Here's a polyfill for the Number predicate functions:

"use strict";  Number.isNaN = Number.isNaN ||     n => n !== n; // only NaN  Number.isNumeric = Number.isNumeric ||     n => n === +n; // all numbers excluding NaN  Number.isFinite = Number.isFinite ||     n => n === +n               // all numbers excluding NaN       && n >= Number.MIN_VALUE  // and -Infinity       && n <= Number.MAX_VALUE; // and +Infinity  Number.isInteger = Number.isInteger ||     n => n === +n              // all numbers excluding NaN       && n >= Number.MIN_VALUE // and -Infinity       && n <= Number.MAX_VALUE // and +Infinity       && !(n % 1);             // and non-whole numbers  Number.isSafeInteger = Number.isSafeInteger ||     n => n === +n                     // all numbers excluding NaN       && n >= Number.MIN_SAFE_INTEGER // and small unsafe numbers       && n <= Number.MAX_SAFE_INTEGER // and big unsafe numbers       && !(n % 1);                    // and non-whole numbers 

All major browsers support these functions, except isNumeric, which is not in the specification because I made it up. Hence, you can reduce the size of this polyfill:

"use strict";  Number.isNumeric = Number.isNumeric ||     n => n === +n; // all numbers excluding NaN 

Alternatively, just inline the expression n === +n manually.