The strength of JavaScript arrays lies in the array methods.
Converting Arrays to Strings
The JavaScript method toString() converts an array to a
string of (comma separated) array values.
Example
var fruits = ["Banana", "Orange", "Apple", "Mango"];
document.getElementById("demo").innerHTML = fruits.toString();
Result
Banana,Orange,Apple,Mango
The join() method also joins all array elements into a string.
It behaves just like toString(), but in addition you can specify the separator:
Example
var fruits = ["Banana", "Orange","Apple", "Mango"];
document.getElementById("demo").innerHTML = fruits.join(" * ");
Result
Banana * Orange * Apple * Mango
Popping and Pushing
When you work with arrays, it is easy to remove elements and add
new elements.
This is what popping and pushing is:
Popping items out of an array, or pushing
items into an array.
Popping
The pop() method removes the last element from an array:
Example
var fruits = ["Banana", "Orange", "Apple", "Mango"];
fruits.pop();
// Removes the last element ("Mango") from fruits
The pop() method returns the value that was "popped out":
Example
var fruits = ["Banana", "Orange", "Apple", "Mango"];
var x =
fruits.pop();
// the value of x is "Mango"
Pushing
The push() method adds a new element to an array (at the end):
Example
var fruits = ["Banana", "Orange", "Apple", "Mango"];
fruits.push("Kiwi");
// Adds a new element ("Kiwi") to fruits
The push() method returns the new array length:
Example
var fruits = ["Banana", "Orange", "Apple", "Mango"];
var x =
fruits.push("Kiwi");
// the value of x is 5
Shifting Elements
Shifting is equivalent to popping, working on the first element instead of
the last.
The shift() method removes the first element of an array, and "shifts" all
other elements one place up.
Example
var fruits = ["Banana", "Orange", "Apple", "Mango"];
fruits.shift();
// Removes the first element "Banana" from fruits
The unshift() method adds a new element to an array (at the beginning), and "unshifts"
older elements:
Example
var fruits = ["Banana", "Orange", "Apple", "Mango"];
fruits.unshift("Lemon");
// Adds a new element "Lemon" to fruits
The shift() method returns the string that was "shifted out".
The unshift() method returns the new array length.
Changing Elements
Array elements are accessed using their index number:
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Array indexes start with 0. [0] is the first array element, [1] is the second, [2] is the third .... |
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Example
var fruits = ["Banana", "Orange", "Apple", "Mango"];
fruits[0] = "Kiwi";
// Changes the first element of fruits to "Kiwi"
The length property provides an easy way to append a new element to an array:
Example
var fruits = ["Banana", "Orange", "Apple", "Mango"];
fruits[fruits.length] = "Kiwi";
// Appends "Kiwi" to fruit
Deleting Elements
Since JavaScript arrays are objects, elements can be deleted by using the
JavaScript operator delete:
Example
var fruits = ["Banana", "Orange", "Apple", "Mango"];
delete fruits[0];
// Changes the first element in fruits to undefined
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Using delete on array elements leaves undefined holes in the array. Use pop() or shift() instead. |
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Splicing an Array
The splice() method can be used to add new items to an array:
Example
var fruits = ["Banana", "Orange", "Apple", "Mango"];
fruits.splice(2, 0, "Lemon", "Kiwi");
The first parameter (2) defines the position where new elements should be
added (spliced in).
The second parameter (0) defines how many elements should be
removed.
The rest of the parameters ("Lemon" , "Kiwi") define the new elements to be
added.
Using splice() to Remove Elements
With clever parameter setting, you can use splice() to remove elements without leaving
"holes" in the array:
Example
var fruits = ["Banana", "Orange", "Apple", "Mango"];
fruits.splice(0, 1);
// Removes the first element of fruits
The first parameter (0) defines the position where new elements should be
added (spliced in).
The second parameter (1) defines how many elements should be
removed.
The rest of the parameters are omitted. No new elements will be added.
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:
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.
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
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
Joining Arrays
The concat() method creates a new array by concatenating two arrays:
Example
var myGirls = ["Cecilie", "Lone"];
var myBoys = ["Emil", "Tobias","Linus"];
var myChildren = myGirls.concat(myBoys);
// Concatenates (joins) myGirls and myBoys
The concat() method can take any number of array arguments:
Example
var arr1 = ["Cecilie", "Lone"];
var arr2 = ["Emil", "Tobias","Linus"];
var arr3 = ["Robin", "Morgan"];
var myChildren = arr1.concat(arr2, arr3);
// Concatenates arr1 with arr2 and arr3
Slicing an Array
The slice() method slices out a piece of an array into a new
array.
This example slices out a part of an array starting from array element 1
("Orange"):
Example
var fruits = ["Banana", "Orange", "Lemon", "Apple", "Mango"];
var citrus = fruits.slice(1);
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Array indexes start with 0. [0] is the first array element, [1] is the second, [2] is the third .... |
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This example slices out a part of an array starting from array element 3
("Apple"):
Example
var fruits = ["Banana", "Orange", "Lemon", "Apple", "Mango"];
var citrus = fruits.slice(3);
The slice() method can take two arguments like slice(1,3).
The method then selects elements from the start argument, and up to (but not
including) the end argument.
Example
var fruits = ["Banana", "Orange", "Lemon", "Apple", "Mango"];
var citrus = fruits.slice(1, 3);
If the end argument is omitted, like in the first examples, the slice()
method slices out the rest of the array.
Example
var fruits = ["Banana", "Orange", "Lemon", "Apple", "Mango"];
var citrus = fruits.slice(2);
The valueOf() Method
The valueOf() method is the default behavior for an array.
It converts an array to a primitive value.
JavaScript will automatically convert an array to a string when a primitive value
is expected.
Because of this, all these examples will produce the same result:
Example
var fruits = ["Banana", "Orange", "Apple", "Mango"];
document.getElementById("demo").innerHTML = fruits;
Example
var fruits = ["Banana", "Orange", "Apple", "Mango"];
document.getElementById("demo").innerHTML = fruits.valueOf();
Example
var fruits = ["Banana", "Orange", "Apple", "Mango"];
document.getElementById("demo").innerHTML = fruits.toString();
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All JavaScript objects have the valueOf() and toString() methods. |
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