Loading ...
Sorry, an error occurred while loading the content.

Re: [jslint] Circular Function Definitions

Expand Messages
  • Felix E. Klee
    On Fri, Dec 31, 2010 at 9:49 PM, Rob Richardson ... No, the opposite is true. See the second example in my original post. That works
    Message 1 of 17 , Jan 1, 2011
    • 0 Attachment
      On Fri, Dec 31, 2010 at 9:49 PM, Rob Richardson <erobrich@...>
      wrote:
      > If you put var f = function () {... before function callback(... then
      > JSLint would likely be fine.

      No, the opposite is true. See the second example in my original post.
      That works fine with JSLint. Changing the order would make JSLint
      complain about "callback" not being defined.

      But that's not really the issue.

      > The secondary concern is that you're passing in a flag that says
      > whether you should use a follow-up function.

      The code is more complicated in reality. There is a lot happening in
      "f", and whether to send another request to the server is determined
      based not just on the state of "moreToDo".

      The code chains XHRs, to download server generated data.

      > Passing the function to run into callback() instead of a flag makes
      > callback() more generic, and makes this point a bit more clear, and
      > that was the focus of Erik's thoughts.

      Erik's code would just generate an infinite loop, because it evaluates
      to:

      f = function () {
      sendToServer('xyz', f);
      };

      But that's *all* besides the point. My question, I think, can be
      summarized to:

      For the sake of consistency, and thus readability, should I always
      define functions as:

      var f;

      // ...

      f = function () {
      // ...
      }

      instead of the short form:

      function f() {
      // ..
      }

      ?

      Furthermore, can this be enforced with JSLint?
    • Felix E. Klee
      On Sat, Jan 1, 2011 at 11:59 AM, Felix E. Klee ... Sorry, that should be: There is a lot happening in callback
      Message 2 of 17 , Jan 1, 2011
      • 0 Attachment
        On Sat, Jan 1, 2011 at 11:59 AM, Felix E. Klee <felix.klee@...>
        wrote:
        > There is a lot happening in "f"

        Sorry, that should be:

        There is a lot happening in "callback"
      • Rob Richardson
        Ah, I see I may have misunderstood. You re proposing the following: var a,b; a = function () { // ... b(); // ... } b = function () { // ... a(); // ... } Is
        Message 3 of 17 , Jan 1, 2011
        • 0 Attachment
          Ah, I see I may have misunderstood. You're proposing the following:

          var a,b;

          a = function () {
          // ...
          b();
          // ...
          }

          b = function () {
          // ...
          a();
          // ...
          }

          Is this the dilemma at hand?

          Rob


          -----Original Message-----
          From: jslint_com@yahoogroups.com [mailto:jslint_com@yahoogroups.com] On
          Behalf Of Felix E. Klee
          Sent: Saturday, January 01, 2011 3:59 AM
          To: jslint_com@yahoogroups.com
          Subject: Re: [jslint] Circular Function Definitions

          On Fri, Dec 31, 2010 at 9:49 PM, Rob Richardson <erobrich@...>
          wrote:
          > If you put var f = function () {... before function callback(... then
          > JSLint would likely be fine.

          No, the opposite is true. See the second example in my original post.
          That works fine with JSLint. Changing the order would make JSLint
          complain about "callback" not being defined.

          But that's not really the issue.

          > The secondary concern is that you're passing in a flag that says
          > whether you should use a follow-up function.

          The code is more complicated in reality. There is a lot happening in
          "f", and whether to send another request to the server is determined
          based not just on the state of "moreToDo".

          The code chains XHRs, to download server generated data.

          > Passing the function to run into callback() instead of a flag makes
          > callback() more generic, and makes this point a bit more clear, and
          > that was the focus of Erik's thoughts.

          Erik's code would just generate an infinite loop, because it evaluates
          to:

          f = function () {
          sendToServer('xyz', f);
          };

          But that's *all* besides the point. My question, I think, can be
          summarized to:

          For the sake of consistency, and thus readability, should I always
          define functions as:

          var f;

          // ...

          f = function () {
          // ...
          }

          instead of the short form:

          function f() {
          // ..
          }

          ?

          Furthermore, can this be enforced with JSLint?
        • Felix E. Klee
          ... Yes. To me it seems reasonable to - for consistency - avoid the short form: function f() { // ... } And I would like to enforce that in the entire project,
          Message 4 of 17 , Jan 3, 2011
          • 0 Attachment
            On Sun, Jan 2, 2011 at 4:54 AM, Rob Richardson <erobrich@...> wrote:
            > var a,b;
            >
            > a = function () {
            > // ...
            > b();
            > // ...
            > }
            >
            > b = function () {
            > // ...
            > a();
            > // ...
            > }
            >
            > Is this the dilemma at hand?

            Yes.

            To me it seems reasonable to - for consistency - avoid the short form:

            function f() {
            // ...
            }

            And I would like to enforce that in the entire project, with JSLint.
            However, as JSLint does not offer a corresponding option, I wonder if I
            am on the wrong track, overdoing things.
          • Erik Eckhardt
            My apologies. My code was written too hastily. I thought you were using a Boolean to indicate whether to make the return call to f. The point I was trying to
            Message 5 of 17 , Jan 3, 2011
            • 0 Attachment
              My apologies. My code was written too hastily. I thought you were using a
              Boolean to indicate whether to make the return call to f.

              The point I was trying to get across is that you don't need the circularity.

              There are many ways to solve this. Here's one: Any time you want something
              to happen after the callback, pass the call to the callback in an anonymous
              function:

              f = function() {
              ___// do stuff
              ___xhr(params, callback); // plain call to cb func
              ___xhr(params, function() {callback(); f();}); // circular call back to f
              }

              Or pass the after-callback function as a parameter to the callback function
              (again through use of an anonymous function).

              or: `callback.returnfn = f; // now check property in that function and call
              if needed

              Or use a library like jquery and define a custom event, then bind all the
              handlers to the event you want, and trigger it any time.

              Circularity isn't required.

              Erik

              On Fri, Dec 31, 2010 at 12:12 PM, Felix E. Klee <felix.klee@...> wrote:

              >
              >
              > On Fri, Dec 31, 2010 at 7:21 PM, Erik Eckhardt <erik@...<erik%40eckhardts.com>>
              > wrote:
              > > function callback(morefn) {
              > > // do something ...
              > > if (typeof(morefn) === 'function') {
              > > moref();
              > > }
              > > }
              > >
              > > f = function () {
              > > sendToServer('xyz', callback ? f : null);
              > > };
              >
              > Are you sure this makes sense? The second last line will always evaluate
              > to:
              >
              > sendToServer('xyz', f);
              >
              > And I don't see how this solves the issue I raised:
              >
              > var f;
              >
              > function callback(moreToDo) {
              > // ...
              > }
              >
              > f = function () {
              > // ...
              > };
              >
              > That's inconsistent, and thus confusing. Of course one could write:
              >
              > var callback, f;
              >
              > callback = function (moreToDo) {
              > // ...
              > };
              >
              > f = function () {
              > // ...
              > };
              >
              > Now things are consistent. But is that the way to go?
              >
              >


              [Non-text portions of this message have been removed]
            • Felix E. Klee
              ... No, that was correct. In the example code, I *was* using a boolean. Only in the real code, things are more complex: Based on what the XHR returns some
              Message 6 of 17 , Jan 4, 2011
              • 0 Attachment
                On Tue, Jan 4, 2011 at 7:53 AM, Erik Eckhardt <erik@...> wrote:
                > I thought you were using a Boolean to indicate whether to make the
                > return call to f.

                No, that was correct. In the example code, I *was* using a boolean. Only
                in the real code, things are more complex:

                Based on what the XHR returns some calculations are performed, and - if
                needed - another XHR is made.

                > The point I was trying to get across is that you don't need the
                > circularity.

                What's bad about the circularity?

                > xhr(params, function() {callback(); f();}); // circular call back to f

                That would again be an infinite loop. The body of the anonymous function
                would need to be at least slightly more complex. I don't think this is
                increases readability.
              • Erik Eckhardt
                If your example isn t the full story, please post an example of the full story! One thing that s wrong with the circularity is the cross-dependence as JSLint
                Message 7 of 17 , Jan 4, 2011
                • 0 Attachment
                  If your example isn't the full story, please post an example of the full
                  story!

                  One thing that's wrong with the circularity is the cross-dependence as
                  JSLint is showing you. It's not a huge deal, but an annoying one, perhaps.

                  In any case I thought you might find it useful to use some of the techniques
                  I mentioned, where if a function determines that an additional step is
                  needed, it manages it within the function rather than making the callback
                  function have a hard coded reference back. The scheme you're using now seems
                  to make sense but as your application grows you may find that it becomes
                  unworkable. For example, what if you eventually have two functions that may
                  or may not need to be called after an xhr? Are you going to pass two
                  booleans? Or God forbid, a code indicating which functions to run? If from
                  the start you simply passed around single callback functions (which
                  themselves could be a string of functions) this problem would be solved.

                  function myxhr(url, params, callback) {
                  ___//do stuff;
                  doXhr(function() {myxhrreturn(xmlhttp, callback):});
                  }

                  function myxhrreturn(xmlhttp, callback) {
                  ___//process xmlhttp object into a result
                  ___callback(result);
                  }

                  function getsomething() {
                  ___myxhr('http://example.com', 'a=1', function(result) {
                  ______if (result.blah === 'gorp') {
                  _________dosomething;
                  ______} else {
                  _________dosomethingelse();
                  ______}
                  ___}
                  }

                  Now your getsomething function controls everything and all your xmlhttp
                  requests can be handled the same way without having to make a hardcoded
                  call. If you want the logic in the myxhrreturn function, you can put it
                  there, but it's not required. Here's another way to do it:

                  function getsomething() {
                  var cb;
                  if (somecondition) {
                  ______cb = function(result) {dosomething(result)};
                  ___} else {
                  ______cb = function(result) {dosomethingelse(result);};
                  ___}
                  ___myxhr('http://example.com', 'a=1', cb}
                  }

                  See how versatile this is? You only need a single callback, no extra Boolean
                  parameter is needed to indicate whether to call a hard-coded function name.
                  Any time you want more stuff to happen, you can load it into the passed
                  callback function somehow.

                  Erik

                  On Tue, Jan 4, 2011 at 1:47 AM, Felix E. Klee <felix.klee@...> wrote:

                  >
                  >
                  > On Tue, Jan 4, 2011 at 7:53 AM, Erik Eckhardt <erik@...<erik%40eckhardts.com>>
                  > wrote:
                  > > I thought you were using a Boolean to indicate whether to make the
                  > > return call to f.
                  >
                  > No, that was correct. In the example code, I *was* using a boolean. Only
                  > in the real code, things are more complex:
                  >
                  > Based on what the XHR returns some calculations are performed, and - if
                  > needed - another XHR is made.
                  >
                  >
                  > > The point I was trying to get across is that you don't need the
                  > > circularity.
                  >
                  > What's bad about the circularity?
                  >
                  >
                  > > xhr(params, function() {callback(); f();}); // circular call back to f
                  >
                  > That would again be an infinite loop. The body of the anonymous function
                  > would need to be at least slightly more complex. I don't think this is
                  > increases readability.
                  >
                  >


                  [Non-text portions of this message have been removed]
                • Felix E. Klee
                  On Tue, Jan 4, 2011 at 7:35 PM, Erik Eckhardt ... There may be a misunderstanding. Thus, for your pleasure, below a more real-life
                  Message 8 of 17 , Jan 5, 2011
                  • 0 Attachment
                    On Tue, Jan 4, 2011 at 7:35 PM, Erik Eckhardt <erik@...>
                    wrote:
                    > no extra Boolean parameter is needed to indicate whether to call a
                    > hard-coded function name.

                    There may be a misunderstanding.

                    Thus, for your pleasure, below a more real-life example. Asides from
                    being more verbose, the only difference to my original example is the
                    addition of the parameter "liveCommentary". Together with the flag
                    "matchIsStillRunning" (formerly: "moreToDo") it forms the data returned
                    from the server.

                    var sendToServer; // defined elsewhere

                    function onCommentaryReceived(commentary, matchIsStillRunning) {
                    // write live commentary: ...
                    if (matchIsStillRunning) {
                    requestCommentary();
                    }
                    }

                    function requestCommentary() {
                    sendToServer('Berlin:Munich', onCommentaryReceived);
                    }

                    Naturally, one could rewrite this:

                    var sendToServer; // defined elsewhere

                    function requestCommentary() {
                    sendToServer('Berlin:Munich',
                    function (commentary, matchIsStillRunning) {
                    // write live commentary: ...
                    if (matchIsStillRunning) {
                    requestCommentary();
                    }
                    });
                    }

                    The second form avoids the circular function definition, but is it more
                    readable?
                  • Jordan
                    I think the confusion here is that you shouldn t be using the circular function pattern you are using. In addition, you are using function declarations
                    Message 9 of 17 , Jan 5, 2011
                    • 0 Attachment
                      I think the confusion here is that you shouldn't be using the "circular function" pattern you are using. In addition, you are using function declarations rather than assigning a function statement to a variable.

                      What you want to do, it seems, is immediately run requestCommentary after a matchIsStillRunning response comes back from the server.

                      What I can think of off the top of my head is:

                      var onCommentaryReceived = function (commentary, matchIsStillRunning) {
                      // write live commentary: ...
                      if (matchIsStillRunning) {
                      sendToServer('Berlin:Munich', onCommentaryReceived);
                      }
                      },
                      requestCommentary = function () {
                      return onCommentaryReceived(null, true);
                      };

                      Alternatively, and with less refactoring:
                      var onCommentaryReceived, requestCommentary;
                      onCommentaryReceived = function (commentary, matchIsStillRunning) {
                      // write live commentary: ...
                      if (matchIsStillRunning) {
                      requestCommentary();
                      }
                      };
                      requestCommentary = function () {
                      sendToServer('Berlin:Munich', onCommentaryReceived);
                      };

                      --- In jslint_com@yahoogroups.com, "Felix E. Klee" <felix.klee@...> wrote:
                      >
                      > On Tue, Jan 4, 2011 at 7:35 PM, Erik Eckhardt <erik@...>
                      > wrote:
                      > > no extra Boolean parameter is needed to indicate whether to call a
                      > > hard-coded function name.
                      >
                      > There may be a misunderstanding.
                      >
                      > Thus, for your pleasure, below a more real-life example. Asides from
                      > being more verbose, the only difference to my original example is the
                      > addition of the parameter "liveCommentary". Together with the flag
                      > "matchIsStillRunning" (formerly: "moreToDo") it forms the data returned
                      > from the server.
                      >
                      > var sendToServer; // defined elsewhere
                      >
                      > function onCommentaryReceived(commentary, matchIsStillRunning) {
                      > // write live commentary: ...
                      > if (matchIsStillRunning) {
                      > requestCommentary();
                      > }
                      > }
                      >
                      > function requestCommentary() {
                      > sendToServer('Berlin:Munich', onCommentaryReceived);
                      > }
                      >
                      > Naturally, one could rewrite this:
                      >
                      > var sendToServer; // defined elsewhere
                      >
                      > function requestCommentary() {
                      > sendToServer('Berlin:Munich',
                      > function (commentary, matchIsStillRunning) {
                      > // write live commentary: ...
                      > if (matchIsStillRunning) {
                      > requestCommentary();
                      > }
                      > });
                      > }
                      >
                      > The second form avoids the circular function definition, but is it more
                      > readable?
                      >
                    • Felix E. Klee
                      ... The question is: Why? Is that considered bad practice? If so, a reference please. ... See my original post. There I mentioned that I would like to enforce
                      Message 10 of 17 , Jan 6, 2011
                      • 0 Attachment
                        On Thu, Jan 6, 2011 at 6:27 AM, Jordan <ljharb@...> wrote:
                        > I think the confusion here is that you shouldn't be using the
                        > "circular function" pattern you are using.

                        The question is: Why? Is that considered bad practice? If so, a
                        reference please.

                        > In addition, you are using function declarations rather than assigning
                        > a function statement to a variable.

                        See my original post. There I mentioned that I would like to enforce
                        that convention for the whole project using JSLint. Only I wonder why
                        there is no such option.

                        > What I can think of off the top of my head is:
                        >
                        > [...]
                        > requestCommentary = function () {
                        > return onCommentaryReceived(null, true);
                        > };

                        That would work, but it's confusing to read. At least the function name
                        "onCommentaryReceived" should be changed.

                        > Alternatively, and with less refactoring:

                        See my original post. It's there already.
                      • Felix E. Klee
                        On Fri, Dec 31, 2010 at 6:33 PM, Felix E. Klee ... Just figured that this is akin to: http://en.wikipedia.org/wiki/Mutual_recursion And I
                        Message 11 of 17 , Jan 8, 2011
                        • 0 Attachment
                          On Fri, Dec 31, 2010 at 6:33 PM, Felix E. Klee <felix.klee@...>
                          wrote:
                          > If I write code such as the following

                          Just figured that this is akin to:

                          http://en.wikipedia.org/wiki/Mutual_recursion

                          And I checked: The latest version of JSLint, 2011-01-06, still
                          complains about an undefined function.
                        • Douglas Crockford
                          ... ` var sendToServer; ` ` function f() { ` sendToServer( xyz , function (moreToDo) { ` // do something ... ` if (moreToDo) { `
                          Message 12 of 17 , Jan 8, 2011
                          • 0 Attachment
                            --- In jslint_com@yahoogroups.com, "Felix E. Klee" <felix.klee@...> wrote:
                            >
                            > If I write code such as the following, then JSLint complains that "f" is
                            > not defined.
                            >
                            > var sendToServer;
                            >
                            > function callback(moreToDo) {
                            > // do something ...
                            > if (moreToDo) {
                            > f();
                            > }
                            > }
                            >
                            > function f() {
                            > sendToServer('xyz', callback);
                            > }
                            >
                            > What's the most elegant solution to get rid of the error message?


                            ` var sendToServer;
                            `
                            ` function f() {
                            ` sendToServer('xyz', function (moreToDo) {
                            ` // do something ...
                            ` if (moreToDo) {
                            ` f();
                            ` }
                            ` });
                            ` }
                          • Felix E. Klee
                            On Sat, Jan 8, 2011 at 4:05 PM, Douglas Crockford ... Thanks for the suggestion! I guess I ll take this approach and put the lengthy do something into a
                            Message 13 of 17 , Jan 8, 2011
                            • 0 Attachment
                              On Sat, Jan 8, 2011 at 4:05 PM, Douglas Crockford
                              <douglas@...> wrote:
                              > ` var sendToServer;
                              > `
                              > ` function f() {
                              > ` sendToServer('xyz', function (moreToDo) {
                              > ` // do something ...
                              > ` if (moreToDo) {
                              > ` f();
                              > ` }
                              > ` });
                              > ` }

                              Thanks for the suggestion! I guess I'll take this approach and put the
                              lengthy "do something" into a separate function.

                              Just thinking about it: I assume that having JSLint to *not* report an
                              error on circular function definitions is non-trivial. That is, if one
                              still wants to be warned about cases were an undefined function would be
                              called, such as:

                              function f() {
                              g();
                              }

                              f();

                              function g() {
                              // do something
                              }
                            Your message has been successfully submitted and would be delivered to recipients shortly.