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
