JavaScript Numbers

• parseInt
  You can convert a string to an integer using the built-in parseInt() function. This takes the base for the conversion as an optional second argument, which you should always provide:

parseInt('123', 10); // 123
parseInt('010', 10); // 10

• Number.isNan
  You can reliably test for NaN using the built-in Number.isNaN() function, which behaves just as its name implies:

Number.isNaN(NaN); // true
Number.isNaN('hello'); // false
Number.isNaN('1'); // false
Number.isNaN(undefined); // false
Number.isNaN({}); // false
Number.isNaN([1]) // false
Number.isNaN([1,2]) // false

• isFinite
  JavaScript also has the special values Infinity and -Infinity:

 1 / 0; //  Infinity
-1 / 0; // -Infinity

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You can test for Infinity, -Infinity and NaN values using the built-in isFinite() function:

isFinite(1 / 0); // false
isFinite(-Infinity); // false
isFinite(NaN); // false