This chapter has focused on the use of functions that you define
yourself. Bear in mind that JavaScript also provides a number of
built-in functions that are part of the language. For example, the
parseInt() function converts a string
to an integer, and the Math.sin() function
computes the sine of a number. For the most part, built-in
functions behave just like user-defined functions: you can assign
them to new variables, object properties, and array elements, and
you can invoke them through these new variable names, properties
or array elements. Practically the only discernible difference
between a built-in function and a user-defined one becomes
apparent when you try to print the value of a built-in function:
the body of the function is replaced with the string "[native
code]", indicating that the function is not itself implemented in
JavaScript.
