How do I check if a JavaScript parameter is a number?

Question

I'm doing some trouble-shooting and want to add a check that a parameter to a function is a number. How do I do this?

Something like this...

function fn(id) {
    return // true iff id is a number else false
}

Even better is if I can check that the parameter is a number AND a valid integer.

Answer 1

function fn(id) {
    return typeof(id) === 'number';
}

To also check if it’s an integer:

function fn(id) {
    return typeof(id) === 'number' &&
            isFinite(id) &&
            Math.round(id) === id;
}

Answer 2

i'd say

 n === parseInt(n)

is enough. note three '===' - it checks both type and value

Answer 3

Check if the type is number, and whether it is an int using parseInt:

if (typeof id == "number" && id == parseInt(id))