JavaScript Array Methods
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
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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
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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
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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"
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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
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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
Try it Yourself »Shifting Elements
Shifting is equivalent to popping, working on the first element instead of the last.
The shift() method removes the first array element and "shifts" all other elements to a lower index.
Example
var fruits = ["Banana", "Orange", "Apple", "Mango"];
fruits.shift();
// Removes the first element "Banana" from fruits
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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
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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"
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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
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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");
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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
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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
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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
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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});
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or
Example
var points = [40, 100, 1, 5, 25, 10];
points.sort(function(a, b){return a>b});
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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});
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or
Example
var points = [40, 100, 1, 5, 25, 10];
points.sort(function(a, b){return b>a});
Try it Yourself »
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
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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
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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
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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
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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);
Try it Yourself »
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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);
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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);
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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);
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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;
Try it Yourself »
Example
var fruits = ["Banana", "Orange", "Apple", "Mango"];
document.getElementById("demo").innerHTML = fruits.valueOf();
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Example
var fruits = ["Banana", "Orange", "Apple", "Mango"];
document.getElementById("demo").innerHTML = fruits.toString();
Try it Yourself »
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All JavaScript objects have the valueOf() and toString() methods. |
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Complete Array Reference
For a complete reference, go to our Complete JavaScript Array Reference.
The reference contains descriptions and examples of all Array properties and methods.
Test Yourself with Exercises!
Exercise 1 » Exercise 2 » Exercise 3 » Exercise 4 » Exercise 5 »