Find the Length of a String, freeCodeCamp Basic Javascript

In this challenge, we learn how to find the length of a string variable, or a string literal. This is done with the .length property. If you add .length at the end of your string variable or string literal, it will give you back how many characters long that string is.

[vivian]

how would you find the length of a first sentence or a second sentence?

[sarthaksrivastav]

Sir why is the default value taken as 0.