Type Conversion in Javascript

Converting to string

String()

It can take null and undefined as arguments without error.

String(null); // 'null'
String(undefined); // 'undefined'

toString()

It throws an error if the variable is set to null or undefined.

null.toString() // Uncaught TypeError: Cannot read properties of null (reading 'toString')
undefined.toString() // Uncaught TypeError: Cannot read properties of null (reading 'toString')

Converting to Number

Number()

This constructor converts an argument to a number.
If the characters in the argument can't be interpreted as a number, it converts the argument to NaN

Number('123px'); // NaN
Number('$123'); // NaN

parseInt() or parseFloat()

It reads the number until it reaches the character that can't be interpreted as a number.

parseInt('12px'); // 12
parseint('$12'); // NaN