Check if a variable contains a numerical value in Javascript?

Question

In PHP, it\'s pretty easy:

is_numeric(23);//true
is_numeric(\"23\");//true
is_numeric(23.5);//true
is_numeric(true);//false

But how do I do

Answer 1

To check types in javascript you can use the typeof operator:

js> var x = 1;
js> typeof(x);
number

So:

if (typeof(x) === 'number') {
   // Do something
}

If you want to coerce the value of a variable to an integer, you can use parseInt(x, 10) which will parse the value as an integer in base 10. Similarly, you can use parseFloat if you want a floating point value. However, these will always coerce regardless of type so passing null, true, etc will always return a number. However, you can check whether its a valid number by calling isNaN.

So, putting it all together:

!isNaN(parseFloat(23)) // true
!isNaN(parseFloat('23')) // true
!isNaN(parseFloat(23.5)) // true
!isNaN(parseFloat(true)) // false

or

function isNumber(x) {
    return !isNaN(parseFloat(x));
}