javascript

Chapter 5: Reference Types
Reordering Methods
Two methods deal directly with the reordering of items already in the array: reverse() and sort() . As
one might expect, the reverse() method simply reverses the order of items in an array. Take this code
for example:
var values = [1, 2, 3, 4, 5];
values.reverse();
alert(values); //5,4,3,2,1
Here, the array values has its items initially set to 1, 2, 3, 4, and 5, in that order. Calling reverse() on
the array reverses the order to 5, 4, 3, 2, 1. This method is fairly straightforward but doesn ’ t provide
much flexibility, which is where the sort() method comes in.
By default, the sort() method puts the items in ascending order — with the smallest value first and the
largest value last. To do this, the sort() method calls the String() casting function on every item and
then compares the strings to determine the correct order. This occurs even if all items in an array are
numbers, as in this example:
var values = [0, 1, 5, 10, 15];
values.sort();
alert(values); //0,1,10,15,5
Even though the values in this example begin in correct numeric order, the sort() method changes that
order based on their string equivalents. So even though 5 is less than 10, the string “ 10 ” comes before
“ 5 ” when doing a string comparison, so the array is updated accordingly. Clearly this is not an optimal
solution in many cases, so the sort() method allows you to pass in a comparison function that indicates
which value should come before which.
A comparison function accepts two arguments and returns a negative number if the first argument
should come before the second, a zero if the arguments are equal, or a positive number if the first
argument should come after the second. Here ’ s an example of a simple comparison function:
function compare(value1, value2) {
if (value1 < value2) {
return -1;
} else if (value1 > value2) {
return 1;
} else {
return 0;
}
}
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