4.3.1 JS Array Methods

Popping

The pop() method removes the last element from an array:

Example 3: JS Arrays The pop() Method

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 4: JS Arrays The pop() Method part 2

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 5: JS Arrays The push() Method part 1

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 6: JS Arrays The push() Method part 2

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 array element and "shifts" all other elements to a lower index.

Example 7: JS Arrays The shift() Method part 1

var fruits = ["Banana", "Orange", "Apple", "Mango"];
fruits.shift();            // Removes the first element "Banana" from fruits

The shift() method returns the string that was "shifted out":

Example 8: JS Arrays The shift() Method part 2

var fruits = ["Banana", "Orange", "Apple", "Mango"];
var x = fruits.shift();    // the value of x is "Banana"

The unshift() method adds a new element to an array (at the beginning), and "unshifts" older elements:

Example 9: JS Arrays The shift() Method part 3

var fruits = ["Banana", "Orange", "Apple", "Mango"];
fruits.unshift("Lemon");    // Adds a new element "Lemon" to fruits

The unshift() method returns the new array length.

Example 10: JS Arrays The shift() Method part 4

var fruits = ["Banana", "Orange", "Apple", "Mango"];
fruits.unshift("Lemon");    // Returns 5

Changing Elements

Array elements are accessed using their index number:

Array indexes start with 0. [0] is the first array element, [1] is the second, [2] is the third ...

Example 11: JS Arrays Bracket Indexing

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 12: JS Arrays The length Property

var fruits = ["Banana", "Orange", "Apple", "Mango"];
fruits[fruits.length] = "Kiwi";          // Appends "Kiwi" to fruits

Deleting Elements

Since JavaScript arrays are objects, elements can be deleted by using the JavaScript operator delete:

Example 13: JS Arrays The delete Method

var fruits = ["Banana", "Orange", "Apple", "Mango"];
delete fruits[0];           // Changes the first element in fruits to undefined

Using delete may leave undefined holes in the array. Use pop() or shift() instead.

Splicing an Array

The splice() method can be used to add new items to an array:

Example 14: JS Arrays The splice() Method part 1

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.
• The splice() method returns an array with the deleted items:

Example 15: JS Arrays The splice() Method part 2

var fruits = ["Banana", "Orange", "Apple", "Mango"];
fruits.splice(2, 2, "Lemon", "Kiwi");

Using splice() to Remove Elements

With clever parameter setting, you can use splice() to remove elements without leaving "holes" in the array:

Example 16: JS Arrays The splice() Method part 3

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.

Merging (Concatenating) Arrays

The concat() method creates a new array by merging (concatenating) existing arrays:

Example 17: Merging Two Arrays

var myGirls = ["Cecilie", "Lone"];
var myBoys = ["Emil", "Tobias", "Linus"];
var myChildren = myGirls.concat(myBoys);   // Concatenates (joins) myGirls and myBoys

• The concat() method does not change the existing arrays. It always returns a new array.
• The concat() method can take any number of array arguments:

Example 17: Merging Three Arrays

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

The concat() method can also take strings as arguments:

Example 18: Merging an Array with Values

var arr1 = ["Emil", "Tobias", "Linus"];
var myChildren = arr1.concat("Peter"); 

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 19: JS Arrays The slice() Method part 1

var fruits = ["Banana", "Orange", "Lemon", "Apple", "Mango"];
var citrus = fruits.slice(1);

The slice() method creates a new array. It does not remove any elements from the source array.

This example slices out a part of an array starting from array element 3 ("Apple"):

Example 20: JS Arrays The slice() Method part 2

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 21: JS Arrays The slice() Method part 3

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 22: JS Arrays The slice() Method part 4

var fruits = ["Banana", "Orange", "Lemon", "Apple", "Mango"];
var citrus = fruits.slice(2);

Automatic toString()

• JavaScript automatically converts an array to a comma separated string when a primitive value is expected.
• This is always the case when you try to output an array.
• These two examples will produce the same result:

Example 23: JS Arrays The toString() Method part 1

var fruits = ["Banana", "Orange", "Apple", "Mango"];
document.getElementById("demo").innerHTML = fruits.toString();

Example 24: JS Arrays The toString() Method part 2

var fruits = ["Banana", "Orange", "Apple", "Mango"];
document.getElementById("demo").innerHTML = fruits;

All JavaScript objects have a toString() method.