# Javascript prompt check number

##### *2020-01-23 18:16*

To check if a variable contains a valid number and not just a String which looks like a number, can be used. This is part of the language since ES2015 Examples:Tour Start here for a quick overview of the site Help Center Detailed answers to any questions you might have Meta Discuss the workings and policies of this site javascript prompt check number

Internally, a number is represented in 64bit format IEEE754, so there are exactly 64 bits to store a number: 52 of them are used to store the digits, 11 of them store the position of the decimal point (they are zero for integer numbers), and 1 bit is for the sign.