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String: length

Strings have the length property. This property represents the number of characters in a string. To do this, you must append .length to the string or to the variable that contains the string:
var charNumber = 'Ai'.length;
'Ai' has 2 characters. So charNumber has the value 2.
var name = 'Weiwei';
charNumber = name.length;
'Weiwei' has 6 characters. charNumber now has the value 6.
charNumber = ''.length;
The empty string has no characters. The value of charNumber is 0.

Exercise

Write a function length that takes a string and returns the number of characters of the string. length('sun') should return 3.