JavaScript Sorting Arrays
The sort() method is one of the strongest array methods.
Sorting an Array
The sort() method sorts an array alphabetically:
Example
var fruits = ["Banana",
"Orange", "Apple", "Mango"];
fruits.sort();
// Sorts the elements of fruits
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Reversing an Array
The reverse() method reverses the elements in an array.
You can use it to sort an array in descending order:
Example
var fruits = ["Banana",
"Orange", "Apple", "Mango"];
fruits.sort();
// Sorts the elements of fruits
fruits.reverse();
// Reverses the order of the elements
»
Numeric Sort
By default, the sort() function sorts values as strings.
This works well for strings ("Apple" comes before
"Banana").
However, if numbers are sorted as strings, "25" is
bigger than "100", because "2" is bigger than
"1".
Because of this, the sort() method will produce incorrect
result when sorting numbers.
You can fix this by providing a compare function:
Example
var points = [40, 100, 1, 5, 25, 10];
points.sort(function(a, b){return a - b});
»
Use the same trick to sort an array descending:
Example
var points = [40, 100, 1, 5, 25, 10];
points.sort(function(a, b){return b - a});
»
The Compare Function
The purpose of the compare function is to define an
alternative sort order.
The compare function should return a negative, zero, or
positive value, depending on the arguments:
function(a, b){return a-b}
When the sort() function compares two values, it sends the
values to the compare function, and sorts the values according to the returned
(negative, zero, positive) value.
Example:
When comparing 40 and 100, the sort() method calls the
compare function(40,100).
The function calculates 40-100, and returns -60 (a negative
value).
The sort function will sort 40 as a value lower than 100.
You can use this code snippet to experiment with numerically
and alphabetically sorting:
<button
onclick="myFunction1()">Sort Alphabetically</button>
<button
onclick="myFunction2()">Sort Numerically</button>
<p id="demo"></p>
<script>
var points = [40, 100, 1, 5, 25, 10];
document.getElementById("demo").innerHTML
= points;
function myFunction1() {
points.sort();
document.getElementById("demo").innerHTML = points;
}
function myFunction2() {
points.sort(function(a, b){return a - b});
document.getElementById("demo").innerHTML = points;
}
</script>
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Sorting an Array in Random Order
Example
var points = [40, 100, 1, 5, 25, 10];
points.sort(function(a, b){return 0.5 - Math.random()});
»
Find the Highest (or Lowest) Value
How to find the highest value in an array?
Example
var points = [40, 100, 1, 5, 25, 10];
points.sort(function(a, b){return b - a});
// now points[0] contains the highest value
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And the lowest:
Example
var points = [40, 100, 1, 5, 25, 10];
points.sort(function(a, b){return a - b});
// now points[0] contains the lowest value
»
Sorting Object Arrays
JavaScript arrays often contain objects:
Example
var cars = [
{type:"Volvo", year:2016},
{type:"Saab", year:2001},
{type:"BMW", year:2010}];
Even if objects have properties of different data types, the
sort() method can be used to sort the array.
The solution is to write a compare function to compare the
property values:
Example
cars.sort(function(a, b){return a.year -
b.year});
»
Comparing string properties is a little more complex::
Example
cars.sort(function(a,
b){
var x
= a.type.toLowerCase();
var y
= b.type.toLowerCase();
if (x
< y) {return -1;}
if (x
> y) {return 1;}
return 0;
});
»
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