Reverse Sort on Second Click - Javascript

I have a function that sorts a json array after a link is clicked (so the function is called using an onclick) and the function works and can sort:

function sortArch(a,b) {
x = eval("a." + sort_type).toLowerCase();  
y = eval("b." + sort_type).toLowerCase();  
return ((x < y) ? -1 : ((x > y) ? 1 : 0));
}

When I click the same button I want the function to reverse sort. The reversing is easy enough:

x = eval("a." + sort_type).toLowerCase();  
y = eval("b." + sort_type).toLowerCase();  
return ((x < y) ? 1 : ((x > y) ? -1 : 0));

My problem is having the function know which way it needs to sort. I was thinking of using a boolean flag, but I can't seem to come up w开发者_如何转开发ith anything that works. I'm only looking for a way to keep track of which way it is sorted and then if the button is clicked it resorts with the second code snippet. Thanks in advanced!

---

You could do something like this:

function mySort(desc) {
  var mod = desc ? -1 : 1;
  return function(a,b) {
    var lca = a[sort_type].toLowerCase(), 
        lcb = b[sort_type].toLowerCase();
    return lca > lcb ? 1 * mod : lca < lcb -1 * mod : 0;
  }
}

arr.sort(mySort(true)); //sort descending
arr.sort(mySort(false)); //sort ascending

btw: try not to use eval when you don't have to, it is slow and messy

---

You're almost done:

function compareFunc(sort_type, ascending) {
    var direction = ascending ? 1 : -1;
    return function(a, b) {
        x = a[sort_type].toLowerCase();
        y = b[sort_type].toLowerCase();

        return direction * x.localeCompare(y);
    }
}

Examples of use:

persons = [
    {firstName: 'John', lastName: 'Foo'},
    {firstName: 'Bob', lastName: 'Bar'}
];


// In your button click events, use compareFunc to generate the right function :
persons.sort(compareFunc('firstName', true));
// or
persons.sort(compareFunc('firstName', false));
// or
persons.sort(compareFunc('lastName', true));
// or
persons.sort(compareFunc('lastName', false));

Cheers!

---

Your idea of using a boolean flag is recommended:

function sort(reverse){
  if(reverse){
    //reverse sort code
  }else{
    //normal sort code
  }
}

bottonElement.onclick = function(){sort(true);}; //or use addEventHandler

This also allows a sort() cass, which automatically does a normal sort since undefined is "falsy".