JAVASCRIPT

check if a variable is a number in javascript

// as test cases we have two variables of which 1 is a number and the second one is a string
let x = 7;
let y = "hello"
let result1 = !Number.isNaN(x) // true
let result2 = !Number.isNaN(y) // flase

check if number is integer js

const int = 10;
const float = 10.5;

console.log(Number.isInteger(int)); // true
console.log(Number.isInteger(float)); // false

// Explanation
// The Number.isInteger() method returns true 
// if a value is an integer of the datatype Number. 
// Otherwise it returns false 
// Source: https://www.w3schools.com/jsref/jsref_isinteger.asp

javascript check if variable is number

function isNumber(n) {
  return !isNaN(parseFloat(n)) && !isNaN(n - 0);
}

javascript check if number

function isNumber(value) {
  return !isNaN(value) && parseFloat(Number(value)) === value && !isNaN(parseInt(value, 10));
}

check if value is number

if(isNaN(num1))
OR:
if(typeof num1 == 'number'){
    document.write(num1 + " is a number <br/>");
 }else{
    document.write(num1 + " is not a number <br/>");
 }

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