Is there a (built-in) way in JavaScript to check if a string is a valid number?

isNaN(num)     // returns true if the variable does NOT contain a valid number

isNaN(123)     // false
isNaN('123')   // false
isNaN('foo')   // true
isNaN('10px')  // true

function isNumeric(num){
    return !isNaN(num)
}

+num              // returns the numeric value of the string, or NaN if the
                  // string isn't purely numeric characters

+'12'             // 12
+'foo'            // NaN
+'12px'           // NaN

parseInt(num)     // extracts a numeric value from the
                  // start of the string, or NaN.

parseInt('12')    // 12
parseInt('aaa')   // NaN
parseInt('12px')  // 12
parseInt('foo2')  // NaN      These last two may be different
parseInt('12a5')  // 12       from what you expected to see.

parseInt(12.345)   // 12
parseInt('12.345') // 12
+'12.345'          // 12.345

+''                // 0
isNaN('')          // false

parseInt('')       // NaN

var num = "987238";

if(num.match(/^d+$/)){
  //valid integer
}else if(num.match(/^d+.d+$/)){
  //valid float
}else{
  //not valid number
}