JAVASCRIPT

javascript check if string is number

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

// can be wrapped for making simple and readable
function isNumeric(num){
  return !isNaN(num)
}

isNumeric(123)         // true
isNumeric('123')       // true
isNumeric('1e10000')   // true (This translates to Infinity, which is a number)
isNumeric('foo')       // false
isNumeric('10px')      // false

js check if string is integer

function isInt(str) {
  return !isNaN(str) && Number.isInteger(parseFloat(str));
}

js check if string is number

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

isNaN(123)         // false
isNaN('123')       // false
isNaN('1e10000')   // false (This translates to Infinity, which is a number)
isNaN('foo')       // true
isNaN('10px')      // true

js check if string is int

function isNumeric(str) {

	// Check if input is string
	if (typeof str != "string")
    	return false

	// Use type coercion to parse the _entirety_ of the string
    // (`parseFloat` alone does not do this).
	// Also ensure that the strings whitespaces fail
	return !isNaN(str) && 
		!isNaN(parseFloat(str)) 
}

how to check if a string is an integer javascript

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

js check if a string is a number

function isNumeric(str) {
  if (typeof str != "string") return false // we only process strings!  
  return !isNaN(str) && // use type coercion to parse the _entirety_ of the string (`parseFloat` alone does not do this)...
         !isNaN(parseFloat(str)) // ...and ensure strings of whitespace fail
}

verify if something is a number javascript

// parseInt is one of those things that you say wtf javascript?
//if you pass to it any argument with number first and letters after, it
// will pass with the first numbers and say yeah this a number wtf?
let myConvertNumber = parseInt('12wtfwtfwtf');
console.log(myConvertNumber);
// the result is 12 and no error is throw or something
//but this
let myConvertNumber = parseInt('wtf12wtf');
console.log(myConvertNumber);
// is NaN wtf?
//if you truly want an strict way to know if something is really a real number
// use Number() instead
let myConvertNumber = Number('12wtf');
console.log(myConvertNumber);
// with this if the string has any text the result will be NaN

Check Whether Variable Is String Or Number In JavaScript

typeof "ssss"