Prepare array for sorting in closure

问题

According to my research and googling, Javascript seems to lack support for locale aware sorting and string comparisons. There is localeCompare(), but it has been reported of browser specific differencies and impossibility to explicitly set which locale is used (the OS locale is not always the one wanted). There is some intentions to add collation support inside ECMAScript, but before it, we are on our own. And depending how consistent the results are across browsers, may be we are on our own forever :(.

I have the following code, which makes alphabetical sort of an array. It's made speed in mind, and the ideas are got from https://stackoverflow.com/a/11598969/1691517, to which I made some speed improvements.

In this example, the words array has 13 members and the sort-function is called 34 times. I want to replace some of the letters in the words-array (you don't have to know what replacements are made, because it's not the point in this question). If I make these replacements in sort-function ( the one that starts with return function(a, b) ), the code is inefficient, because replacements are made more than once per array member. Of course I can make these replacements outside of this closure, I mean before the line words.sort(sortbyalphabet_timo);, but it's not what I want.

Question 1: Is it possible to modify the words-array in between the lines "PREPARATION STARTS" and "PREPARATION ENDS" so that the sort function uses modified words-array?

Question 2: Is it possible to input arguments to the closure so that code between PREPARATION STARTS and PREPARATION ENDS can use them? I have tried this without success:

var caseinsensitive = true;
words.sort( sortbyalphabet_timo(caseinsensitive) );

And here is finally the code example, and the ready to run example is in http://jsfiddle.net/3E7wb/:

var sortbyalphabet_timo = (function() {
  // PREPARATION STARTS
  var i, alphabet = "-0123456789AaÀàÁáÂâÃãÄäBbCcÇçDdEeÈèÉéÊêËëFfGgHhIiÌìÍíÎîÏïJjKkLlMmNnÑñOoÒòÓóÔôÕõÖöPpQqRrSsTtUuÙùÚúÛûÜüVvWwXxYyÝýŸÿZz",
  index = {};

  i = alphabet.length;
  while (i--) index[alphabet.charCodeAt(i)] = i;
  // PREPARATION ENDS

  return function(a, b) {
    var i, len, diff;

    if (typeof a === "string" && typeof b === "string") {
      (a.length > b.length) ? len = a.length : len = b.length;
      for (i = 0; i < len; i++) {
        diff = index[a.charCodeAt(i)] - index[b.charCodeAt(i)];

        if (diff !== 0) {
          return diff;
        }
      }
      // sort the shorter first
      return a.length - b.length;
    } else {
      return 0;
    }
  };
})();

var words = ['tauschen', '66', '55', '33', 'täuschen', 'andern', 'ändern', 'Ast', 'Äste', 'dosen', 'dösen', 'Donaudam-0', 'Donaudam-1'];
$('#orig').html(words.toString());
words.sort(sortbyalphabet_timo);
$('#sorted').html(words.toString());`

回答1:

Is it possible to modify the words-array in between the lines "PREPARATION STARTS" and "PREPARATION ENDS" so that the sort function uses modified words-array?

No, not really. You don't have access to the array itself, your function only builds the compare-function that is later used when .sort is invoked on the array. If you needed to alter the array, you'll need to write a function that gets it as an argument; for example you could add a method on Array.prototype. It would look like

function mysort(arr) {
    // Preparation
    // declaration of compare function
    // OR execution of closure to get the compare function
    arr.sort(comparefn);
    return arr;
}

Is it possible to input arguments to the closure so that code between PREPARATION STARTS and PREPARATION ENDS can use them?

Yes, of course - that is the reason to use closures :-) However, you can't use sortbyalphabet_timo(caseinsensitive) with your current code. The closure you have is immediately invoked (called an IIFE) and returns the compare-function, which you pass into sort as in your demo.

If you want sortbyalphabet_timo to be the closure instead of the result, you have to remove the brackets after it. You also you can use arguments there, which are accessible in the whole closure scope (including the comparefunction):

var sortbyalphabet_timo_closure = function(caseinsensitive) {
    // Preparation, potentially using the arguments
    // Declaration of compare function, potentially using the arguments
    return comparefn;
}
// then use
words.sort(sortbyalphabet_timo_closure(true));

Currently, you are doing this:

var sortbyalphabet_timo_closure = function(/*having no arguments*/) {
    // Preparation, potentially using the arguments
    // Declaration of compare function, potentially using the arguments
    return comparefn;
}
var sortbyalphabet_timo = sortbyalphabet_timo_closure();
// then use
words.sort(sortbyalphabet_timo);

…which just caches the result of executing the closure, if you'd need to sort multiple times.

来源：https://stackoverflow.com/questions/12606722/prepare-array-for-sorting-in-closure

标签

javascript

sorting

unicode

collation

alphabet