The return Statement
- The code outside of the function doesn’t see its local variables.
- Variable scope refers to how visible variables are to different parts of the program.
- Now we’ve covered the basics, so we actually can start creating and using them.
- In other words, the inner function contains the scope of the outer function.
- Parameters act as local placeholder variables for the values that will be passed into the function as inputs when the function is called.
- Since a nested function is a closure, this means that a nested function can “inherit” the arguments and variables of its containing function.
For example, the jQuery framework defines a function with $. CheckPermission – would be bad if it displays the access granted/denied message . CreateForm – would be bad if it modifies the document, adding a form to it .
If a Function node does asynchronous work with a message, the runtime will not automatically know when it has finished handling the message. In the following example, msg1, msg2, msg3 will be sent to the first output.msg4 will be sent to the second output. Other nodes may attach their own properties to the message, and they should be described in their documentation.
Sometimes people refer to such code as self-describing. Generally function names should be concise and descriptive.
With prefixes in place, a glance at a function name gives an understanding what kind of work it does and what kind of value it returns. For instance, functions that start with “show” usually show something. It is a widespread practice to start a function with a verbal prefix which vaguely describes the action. There must be an agreement within the team on the meaning of the prefixes. To create a function we can use a function declaration.
- The first argument passed to the callback, err, is only set if an error occurred when accessing context.
- But if that variable was defined inside the function, it would have local scope and it would be limited and visible only in the function where it was defined.
- (See the Function object.) The call() and apply() methods can be used to achieve this goal.
- A function can return a literal value or another function.
To help it do so, the Function node should call node.done() at the appropriate time. This will allow the runtime to properly track messages through the system. If the function needs to perform an asynchronous action before sending a message it cannot return the message at the end of the function.