type checking in javascript
A variable will never be an integer type in JavaScript — it doesn't distinguish between different types of Number.
You can test if the variable contains a number, and if that number is an integer.
(typeof foo === "number") && Math.floor(foo) === foo
If the variable might be a string containing an integer and you want to see if that is the case:
foo == parseInt(foo, 10)
These days, ECMAScript 6 (ECMA-262) is "in the house". Use Number.isInteger(x)
to ask the question you want to ask with respect to the type of x:
js> var x = 3
js> Number.isInteger(x)
true
js> var y = 3.1
js> Number.isInteger(y)
false