What is the purpose of atob and btoa method?

“Window” object provides two methods for handling String and  Base 64 encoded string.

window.btoa()

•  This method is for converting a normal string to Bas64 encodes string.
• b(Binary string) to a(Ascii base64 string).
• Example,

var bas64string =  window.btoa('Sandeep');
alert(bas64string);//output U2FuZGVlcA==

window.atob()

• This method is for converting Base64 Ascii string to normal string.
• a(Ascii base64 string) to b(Binary string) .
• Example,

var normalString = window.atob(bas64string);
alert(normalString);//output Sandeep

Fiddle Link:-