JavaScript special statements

This recipe introduces three usages that are rather advantageous and important, try, catch, and finally functions.

Getting ready

We need a new workflow and a scriptable task inside it to try these out.

The example workflow, 06.02 JavaScript special statements, contain all the following examples.

How to do it...

There are two sections in this recipe.

The try, catch, and finally statement

When writing any code, you want to make sure that when the code produces an error, you are still able to execute some critical operations, such as closing an open connection:

  1. Create a scriptable task and enter the following code:
          try { 
        //Main code; 
         System.log("Start Main"); 
         if (error) { 
               throw("Create Error"); 
         } 
         System.log("End Main"); 
      } 
      catch( ex ) { 
        // error handling  
        System.log("Error: "+ex); 
      } finally { 
        //Final Part 
         System.log("Finally"); 
      }
  2. Create an input-parameter of the type Boolean (error) and bind it to the scriptable task.
  3. When executing, you can create an error (throw statements create an intentional error). Without an error, the main code (try) would be executed and then the finally code. When an error is thrown in the main code, the execution (try) will be stopped before "End Main" and then will execute the catch code followed by the finally code.

The function statement

The function command enables us to repeat a program code. A function needs to be defined before it is used, which means that it is placed at the beginning of a program:

  1. Create a scriptable task and enter the following code:
          function functionName (parameter1, parameter2) { 
          // program example 
          parameter3 = parameter1 + parameter2  
          return parameter3 
      }
  2. You now can call the function in the same scriptable task by using:
          result = functionName(2,3);

The call will put the value 2 into parameter1 and the value 3 into parameter2 of the functionName function. The result variable will contain the return value of the function.

How it works...

A typical example where try/catch/finally is used; is to make sure an open connection to a database is closed if an error occurs. Open connections can cause servers to perform slower, rendering them more vulnerable to intrusion or even corrupt data. You would open the connection in the try section and write the close function in the finally section.

If try, catch, and finally are used, you would place the function before the try command. A function is similar to the way an action works. We discussed actions in the recipe Creating actions in this chapter.

See also

See the example workflow 06.02 JavaScript special statements.

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