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## 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

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:

Example

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>

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 contains the highest value

And the lowest:

Example

var points = [40, 100, 1, 5, 25, 10];
points.sort(function(a, b){return a - b});
// now points 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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