Writing Scripts in Nashorn - Scripting in Java: Integrating with Groovy and JavaScript - page 82

Consider the code in Listing 4-2. It defines two functions: isInteger() and
factorial() . The isInteger() function returns true if its argument is an integer;
otherwise, it returns false . The factorial() function computes and returns the
factorial of a natural number. It throws a TypeError is its argument is not a number and a
RangeError if its argument is not a number greater than or equal to 1.
Listing 4-2. The Contents of the factorial.js file
// factorial.js
// Returns true if n is an integer. Otherwise, returns false.
function isInteger(n) {
return typeof n === "number" && isFinite(n) && n%1 === 0;
}
// Define a function that computes and returns the factorial of an integer
function factorial(n) {
if (!isInteger(n)) {
throw new TypeError(
"The number must be an integer. Found:" + n);
}
if(n < 0) {
throw new RangeError(
"The number must be greater than 0. Found: " + n);
}
var fact = 1;
for(var counter = n; counter > 1; fact *= counter--);
return fact;
}
The program in Listing 4-3 uses the factorial() function to compute factorial
for a number and a String. The load() function is used to load the program from the
factorial.js file. The message property of the Error object (or its subtype) contains the
error message. The program uses the message property to display the error message. The
factorial() function throws a TypeError when “Hello” is passed to it as an argument.
The program handles the error and displays the error message.
Listing 4-3. The Contents of the File factorial_test.js
// factorial_test.js
// Load the factorial.js file that contains the factorial() function
load("factorial.js");