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Number

A number can be obtained by directly using a numeric literal such as 345, or with the Number object. The Number object allows you to convert a string to a number.

Applying a numeric operator on a Number object and a numeric literal yields a value of the number type. Numeric operators include addition(+), subtraction(-), multiplication(*), division(/), remainder(%), and recently exponentiation(**).
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<!DOCTYPE html><html><body><script>


   console.log(typeof 100);                      // number
   console.log(typeof new Number(200)); // object
   var n = new Number('300');
   console.log(typeof n);          // object
   console.log(typeof (n**2));  // number
   console.log(n**2);               // 90000
   console.log(new Number("xx"));             // NaN
   console.log(typeof new Number("xx"));   // object

</script></body><html>
This shows a few different ways to convert a string to a number.
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<!DOCTYPE html><html><body><script>


   var s="1000";
   console.log(Number(s)+
                    parseInt(s)+
      (+s)+
      Math.floor(s)+
      Math.round(s));  // 5000

</script></body><html>
This tests if a number is an integer (not a float).
n % 1 === 0

Since ECMAScript 2021, an underscore (_) can be used as a numeric separator to visually group digits in a numeric literal, making long numbers easier to read. It has no effect on the value and works with decimal, binary, octal, hexadecimal, and BigInt literals alike. A separator cannot be leading, trailing, doubled-up, or adjacent to a decimal point.


console.log(1_000_000 === 1000000);
console.log(1_000_000.000_1);
console.log(0b1010_0001);   // binary
console.log(0xA0_B0);       // hex
console.log(123_456n);      // BigInt

// console.log(1__000);   // SyntaxError: only one underscore allowed between digits
// console.log(_1000);    // not a numeric separator; parsed as an identifier

true 1000000.0001 161 41136 123456n