How to Check If a Value Is a Number

console.log(!isNaN(+"54"));
console.log(!isNaN(+"23xede"));
console.log(!isNaN(+"test"));

Check if value is a number

Simple:

if(_myValue is Number)
{
    fire();

}// end if

[UPDATE]

Keep in mind that if _myValue is of type int or uint, then (_myValue is Number) will also equate to true. If you want to know if _myValue is a number that isn't an integer(int) or unsigned integer (uint), in other words a float, then you can simply modify the conditional as follows:

(_myValue is Number && !(_myValue is int) && !(_myValue is uint))

Let's look at an example:

package 
{
    import flash.display.Sprite;
    import flash.events.Event;

    public class Main extends Sprite 
    {

        public function Main():void 
        {
            if (stage) init();
            else addEventListener(Event.ADDED_TO_STAGE, init);
        }

        private function init(e:Event = null):void 
        {
            removeEventListener(Event.ADDED_TO_STAGE, init);

            var number1:Object = 1; // int
            var number2:Object = 1.1; // float
            var number3:Object = 0x000000; // uint

            trace(number1 is Number); // true
            trace(number2 is Number); // true
            trace(number3 is Number); // true

            trace(number1 is Number && !(number1 is int) && !(number1 is uint)); // false
            trace(number2 is Number && !(number2 is int) && !(number2 is uint)); // true
            trace(number3 is Number && !(number3 is int) && !(number3 is uint)); // false

        }

    }

}

How to check if string input is a number?

Simply try converting it to an int and then bailing out if it doesn't work.

try:
    val = int(userInput)
except ValueError:
    print("That's not an int!")

See Handling Exceptions in the official tutorial.

How to check if a String is numeric in Java

With Apache Commons Lang 3.5 and above: NumberUtils.isCreatable or StringUtils.isNumeric.

With Apache Commons Lang 3.4 and below: NumberUtils.isNumber or StringUtils.isNumeric.

You can also use StringUtils.isNumericSpace which returns true for empty strings and ignores internal spaces in the string. Another way is to use NumberUtils.isParsable which basically checks the number is parsable according to Java. (The linked javadocs contain detailed examples for each method.)

Check whether variable is number or string in JavaScript

If you're dealing with literal notation, and not constructors, you can use typeof:.

typeof "Hello World"; // string
typeof 123;           // number

If you're creating numbers and strings via a constructor, such as var foo = new String("foo"), you should keep in mind that typeof may return object for foo.

Perhaps a more foolproof method of checking the type would be to utilize the method found in underscore.js (annotated source can be found here),

var toString = Object.prototype.toString;

_.isString = function (obj) {
  return toString.call(obj) == '[object String]';
}

This returns a boolean true for the following:

_.isString("Jonathan"); // true
_.isString(new String("Jonathan")); // true

In Typescript, How to check if a string is Numeric

The way to convert a string to a number is with Number, not parseFloat.

Number('1234') // 1234
Number('9BX9') // NaN

You can also use the unary plus operator if you like shorthand:

+'1234' // 1234
+'9BX9' // NaN

Be careful when checking against NaN (the operator === and !== don't work as expected with NaN). Use:

 isNaN(+maybeNumber) // returns true if NaN, otherwise false

How to check if a variable is an integer in JavaScript?

Use the === operator (strict equality) as below,

if (data === parseInt(data, 10))
    alert("data is integer")
else
    alert("data is not an integer")

How do I test if a variable is a number in Bash?

One approach is to use a regular expression, like so:

re='^[0-9]+$'
if ! [[ $yournumber =~ $re ]] ; then
   echo "error: Not a number" >&2; exit 1
fi

If the value is not necessarily an integer, consider amending the regex appropriately; for instance:

^[0-9]+([.][0-9]+)?$

...or, to handle numbers with a sign:

^[+-]?[0-9]+([.][0-9]+)?$

Identify if a string is a number

int n;
bool isNumeric = int.TryParse("123", out n);

Update As of C# 7:

var isNumeric = int.TryParse("123", out int n);

or if you don't need the number you can discard the out parameter

var isNumeric = int.TryParse("123", out _);

The var s can be replaced by their respective types!

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