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

Re: [jslint] new Array(n)

Expand Messages
  • Randy Cox
    ... Will you share this useful case, or must it remain a mystery? --Randy -- Randy Cox Senior UI Engineer Compendium Blogware
    Message 1 of 11 , Jun 2, 2009
    • 0 Attachment
      On Tue, Jun 2, 2009 at 4:10 PM, Douglas Crockford <douglas@...> wrote:
      > But then someone showed be a case where new Array(n) is actually useful.

      Will you share this useful case, or must it remain a mystery?

      --Randy

      --
      Randy Cox
      Senior UI Engineer
      Compendium Blogware
    • Michael Lorton
      I believe the useful case is where the argument is a integer. My own opinion would be that that case isn t useful enough to justify allowing the construct at
      Message 2 of 11 , Jun 2, 2009
      • 0 Attachment
        I believe the useful case is where the argument is a integer. My own opinion would be that that case isn't useful enough to justify allowing the construct at all (especially since the type of the argument might not be statically detectable), but of course, it isn't my system.

        M.





        ________________________________
        From: Randy Cox <rcox@...>
        To: jslint_com@yahoogroups.com
        Sent: Tuesday, June 2, 2009 1:17:48 PM
        Subject: Re: [jslint] new Array(n)

        On Tue, Jun 2, 2009 at 4:10 PM, Douglas Crockford <douglas@...> wrote:
        > But then someone showed be a case where new Array(n) is actually useful.

        Will you share this useful case, or must it remain a mystery?

        --Randy

        --
        Randy Cox
        Senior UI Engineer
        Compendium Blogware


        ------------------------------------

        Yahoo! Groups Links



        [Non-text portions of this message have been removed]
      • Douglas Crockford
        ... Suppose you need to construct a string containing n asterisks. It seems the fastest way to do that is new Array(n + 1).join( * )
        Message 3 of 11 , Jun 3, 2009
        • 0 Attachment
          --- In jslint_com@yahoogroups.com, Randy Cox <rcox@...> wrote:
          >
          > On Tue, Jun 2, 2009 at 4:10 PM, Douglas Crockford <douglas@...> wrote:
          > > But then someone showed be a case where new Array(n) is actually useful.
          >
          > Will you share this useful case, or must it remain a mystery?

          Suppose you need to construct a string containing n asterisks.
          It seems the fastest way to do that is

          new Array(n + 1).join('*')
        • sandyhead25
          By faster do you mean faster for the interpreter to execute or faster for the person can save characters by not using a loop? If you mean anything but the
          Message 4 of 11 , Jun 4, 2009
          • 0 Attachment
            By faster do you mean faster for the interpreter to execute or faster for the person can save characters by not using a loop?

            If you mean anything but the first condition I would say you should still ban the array constructor, because those couple extra characters a person must type is pale in comparison to the potential harm introduced by using a method prone to fault. The whole point of JSLint is to solve that problem literally by mandating style not prone to fault.
          • pauanyu
            ... For reference, here is the way to do this with the array literal: var foo = []; foo.length = n + 1; foo = foo.join( * );
            Message 5 of 11 , Jun 4, 2009
            • 0 Attachment
              --- In jslint_com@yahoogroups.com, "Douglas Crockford" <douglas@...> wrote:
              >
              > Suppose you need to construct a string containing n asterisks.
              > It seems the fastest way to do that is
              >
              > new Array(n + 1).join('*')
              >

              For reference, here is the way to do this with the array literal:

              var foo = [];
              foo.length = n + 1;
              foo = foo.join('*');
            • benxwhite
              Here are the different bits of code that I tested. //Method 1 var cnt = 1000000, char = * , str = new Array(cnt + 1).join(char); //Method 2 var cnt = 1000000,
              Message 6 of 11 , Jun 4, 2009
              • 0 Attachment
                Here are the different bits of code that I tested.

                //Method 1
                var cnt = 1000000,
                char = '*',
                str = new Array(cnt + 1).join(char);


                //Method 2
                var cnt = 1000000,
                char = '*',
                a = [],
                x, str;
                for (x = 0; x < cnt; x += 1) {
                a[x] = char;
                }
                str = a.join('');


                //Method 3
                var cnt = 1000000,
                char = '*',
                a = [],
                x, str;
                for (x = 0; x <= cnt; x += 1) {
                a[x] = '';
                }
                str = a.join('char');


                Looking purely at execution performance, it's really a mixed bag...
                In Firefox & Opera the Method 1 approach is faster.
                However in IE, Safari & Chrome Methods 2 & 3 were faster.

                Looking at this from a coding standpoint, I would say that Method 1 is a most elegant bit of code.



                --- In jslint_com@yahoogroups.com, "sandyhead25" <austin.cheney@...> wrote:
                >
                > By faster do you mean faster for the interpreter to execute or faster for the person can save characters by not using a loop?
                >
                > If you mean anything but the first condition I would say you should still ban the array constructor, because those couple extra characters a person must type is pale in comparison to the potential harm introduced by using a method prone to fault. The whole point of JSLint is to solve that problem literally by mandating style not prone to fault.
                >
              • Merlin
                ... Nice. String.prototype.replicate = function (n) { var a = []; a.length = n + 1; return a.join(this); }; var s = * .replicate(10); print(s); var c = cat ;
                Message 7 of 11 , Jun 4, 2009
                • 0 Attachment
                  --- In jslint_com@yahoogroups.com, "pauanyu" <pcxunlimited@...> wrote:
                  >
                  > --- In jslint_com@yahoogroups.com, "Douglas Crockford" <douglas@> wrote:
                  > >
                  > > Suppose you need to construct a string containing n asterisks.
                  > > It seems the fastest way to do that is
                  > >
                  > > new Array(n + 1).join('*')
                  > >
                  >
                  > For reference, here is the way to do this with the array literal:
                  >
                  > var foo = [];
                  > foo.length = n + 1;
                  > foo = foo.join('*');
                  >

                  Nice.

                  String.prototype.replicate = function (n) {
                  var a = [];
                  a.length = n + 1;
                  return a.join(this);
                  };
                  var s = '*'.replicate(10);
                  print(s);
                  var c = "cat";
                  var t = c.replicate(2);
                  print(t);
                • pauanyu
                  ... I d be interested in seeing how those compare to the array literal: var foo = []; foo.length = n + 1; foo = foo.join( * ); In particular, how it compares
                  Message 8 of 11 , Jun 5, 2009
                  • 0 Attachment
                    --- In jslint_com@yahoogroups.com, "benxwhite" <ben.a.white@...> wrote:
                    >
                    > Here are the different bits of code that I tested.
                    >
                    > //Method 1
                    > var cnt = 1000000,
                    > char = '*',
                    > str = new Array(cnt + 1).join(char);
                    >
                    >
                    > //Method 2
                    > var cnt = 1000000,
                    > char = '*',
                    > a = [],
                    > x, str;
                    > for (x = 0; x < cnt; x += 1) {
                    > a[x] = char;
                    > }
                    > str = a.join('');
                    >
                    >
                    > //Method 3
                    > var cnt = 1000000,
                    > char = '*',
                    > a = [],
                    > x, str;
                    > for (x = 0; x <= cnt; x += 1) {
                    > a[x] = '';
                    > }
                    > str = a.join('char');
                    >
                    >
                    > Looking purely at execution performance, it's really a mixed bag...
                    > In Firefox & Opera the Method 1 approach is faster.
                    > However in IE, Safari & Chrome Methods 2 & 3 were faster.
                    >
                    > Looking at this from a coding standpoint, I would say that Method 1 is a most elegant bit of code.
                    >

                    I'd be interested in seeing how those compare to the array literal:

                    var foo = [];
                    foo.length = n + 1;
                    foo = foo.join('*');

                    In particular, how it compares to Method 1.
                  • benxwhite
                    ... //Method 4 var foo = []; foo.length = n + 1; foo = foo.join( * ); Method 4 compared very similar to Method 1 in speed, and actually slightly faster.
                    Message 9 of 11 , Jun 6, 2009
                    • 0 Attachment
                      --- In jslint_com@yahoogroups.com, "pauanyu" <pcxunlimited@...> wrote:
                      >
                      > --- In jslint_com@yahoogroups.com, "benxwhite" <ben.a.white@> wrote:
                      > >
                      > > Here are the different bits of code that I tested.
                      > >
                      > > //Method 1
                      > > var cnt = 1000000,
                      > > char = '*',
                      > > str = new Array(cnt + 1).join(char);
                      > >
                      > >
                      > > //Method 2
                      > > var cnt = 1000000,
                      > > char = '*',
                      > > a = [],
                      > > x, str;
                      > > for (x = 0; x < cnt; x += 1) {
                      > > a[x] = char;
                      > > }
                      > > str = a.join('');
                      > >
                      > >
                      > > //Method 3
                      > > var cnt = 1000000,
                      > > char = '*',
                      > > a = [],
                      > > x, str;
                      > > for (x = 0; x <= cnt; x += 1) {
                      > > a[x] = '';
                      > > }
                      > > str = a.join('char');
                      > >
                      > >
                      > > Looking purely at execution performance, it's really a mixed bag...
                      > > In Firefox & Opera the Method 1 approach is faster.
                      > > However in IE, Safari & Chrome Methods 2 & 3 were faster.
                      > >
                      > > Looking at this from a coding standpoint, I would say that Method 1 is a most elegant bit of code.
                      > >
                      >
                      > I'd be interested in seeing how those compare to the array literal:
                      >
                      > var foo = [];
                      > foo.length = n + 1;
                      > foo = foo.join('*');
                      >
                      > In particular, how it compares to Method 1.
                      >

                      //Method 4
                      var foo = [];
                      foo.length = n + 1;
                      foo = foo.join('*');

                      Method 4 compared very similar to Method 1 in speed, and actually slightly faster. (approximately 10-40% in my tests)
                      It was not the fastest in every browser, but was the most consistent in performance across browsers.

                      I would suggest Method 4 for best performance, and Method 1 for cleanest.
                    • pauanyu
                      ... Very interesting. I find it unintuitive how using arrays to work with strings can actually be faster than working directly with strings... yet here we are.
                      Message 10 of 11 , Jun 6, 2009
                      • 0 Attachment
                        --- In jslint_com@yahoogroups.com, "benxwhite" <ben.a.white@...> wrote:
                        >
                        > //Method 4
                        > var foo = [];
                        > foo.length = n + 1;
                        > foo = foo.join('*');
                        >
                        > Method 4 compared very similar to Method 1 in speed, and actually slightly faster. (approximately 10-40% in my tests)
                        > It was not the fastest in every browser, but was the most consistent in performance across browsers.
                        >
                        > I would suggest Method 4 for best performance, and Method 1 for cleanest.
                        >

                        Very interesting. I find it unintuitive how using arrays to work with strings can actually be faster than working directly with strings... yet here we are.

                        40% faster, you say? That's impressive, given how both appear to do exactly the same thing. It probably has to do with the fact that "new Array" does different things depending on what you pass to it.
                      Your message has been successfully submitted and would be delivered to recipients shortly.