JavaScript Array Methods
Converting Arrays to Strings The JavaScript method toString() converts an array to a string of (comma separated) array values.
JavaScript Code:
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:
JavaScript Code:
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:
JavaScript Code:
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":
JavaScript Code:
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):
JavaScript Code:
var fruits = ["Banana", "Orange", "Apple", "Mango"];
fruits.push("Kiwi"); // Adds a new element ("Kiwi") to fruits
The push() method returns the new array length:
JavaScript Code:
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.
JavaScript Code:
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":
JavaScript Code:
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:
JavaScript Code:
var fruits = ["Banana", "Orange", "Apple", "Mango"];
fruits.unshift("Lemon"); // Adds a new element "Lemon" to fruits
The unshift() method returns the new array length.
JavaScript Code:
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.
JavaScript Code:
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:
JavaScript Code:
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:
JavaScript Code:
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:
JavaScript Code:
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:
JavaScript Code:
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:
JavaScript Code:
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:
JavaScript Code: (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:
JavaScript Code: (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 (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 code slices out a part of an array starting from array element 1 ("Orange"):
JavaScript Code:
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"):
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.
JavaScript Code:
var fruits = ["Banana", "Orange", "Lemon", "Apple", "Mango"];
var citrus = fruits.slice(1, 3);
If the end argument is omitted, the slice() method slices out the rest of the array.
JavaScript Code:
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 codes will produce the same result.
JavaScript Code:
var fruits = ["Banana", "Orange", "Apple", "Mango"];
document.getElementById("demo").innerHTML = fruits.toString();
JavaScript Code:
var fruits = ["Banana", "Orange", "Apple", "Mango"];
document.getElementById("demo").innerHTML = fruits;
All JavaScript objects have a toString() method.
Resources
You may find the following resources useful:
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