We can check if a variable is a number in multiple ways. ## isNaN We can check by calling isNaN with the variable as the argument. It also detects if a string’s content is a number. For example: isNaN(1) // false isNaN('1') // false isNaN('abc') // true Note: isNaN(null) is true . ### typeof Operator We can use the typeof operator before a variable to check if it’s a number, like so: typeof 1 == 'number' // true typeof '1' == 'number' // false