Using JavaScript to Check if Variable is a Number

One of the easiest ways we can use JavaScript to check if a variable is a number is by using the JavaScript typeof Operator in an if conditional statement.

if ( typeof someVariable == "number" ){
  //The variable IS a number
}

In the code above, someVariable is the variable that we want to check to see if it is a number. typeof someVariable will return “number” if the variable is a number, and therefore the conditional statement will be true.

We can put this code in a function to make checking if a variable is a number very simple.

Here is the function:

function isNumber(variable){
  if ( typeof variable == "number" ){
    return true;
  } else {
    return false;  
  }
};

Our function simply returns true if the variable you enter is a number, and false if not.

Now let’s show some examples of this function is use:

function isNumber(variable){
  if ( typeof variable == "number" ){
    return true;
  } else {
    return false;  
  }
};

var variable1 = 1234;
var variable2 = -853;
var variable3 = "1234";
var variable4 = 156.430393;
var variable5 = 0045865;
var variable6 = .00098;

console.log(isNumber(variable1));
console.log(isNumber(variable2));
console.log(isNumber(variable3));
console.log(isNumber(variable4));
console.log(isNumber(variable5));
console.log(isNumber(variable6));

#Output:
true
true
false
true
true
true

Hopefully this article has been useful for you to learn how to use JavaScript to check if a variable is a number.