null

Note: Don’t miss the notes ref undefined below:

Sample

val = null;
// will print "no":
if(val)
    print('yes');
else
    print('no');

// convert to string will print "null":
print(val + '');

// null evaluates to 0 if used as a number:
print(3 + val);

Note:

• undefined is returned when you use a:

  • variable that has been declared but never had a value assigned to it.

  • object propery that doesn’t exist.

• undefined is not the same as null.

• Although they are different, the == operator considers them equal.

• To distinguish between them use the === operator or the typeof operator.

• When used in a boolean context, it converts to false, when used as a number, it converts to NaN and when used as a string, it converts to undefined.