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Tutorial: Javascript Array Method

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By Emmanuel Chinonso

Web Developer

JavaScript Array Methods

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Converting Arrays to Strings The JavaScript method toString() converts an array to a string of (comma separated) array values.

JavaScript Code:

1var fruits = ["Banana", "Orange", "Apple", "Mango"];
2document.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:

1var fruits = ["Banana", "Orange", "Apple", "Mango"];
2document.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:

1var fruits = ["Banana", "Orange", "Apple", "Mango"];
2fruits.pop(); // Removes the last element ("Mango") from fruits

The pop() method returns the value that was "popped out":

JavaScript Code:

1var fruits = ["Banana", "Orange", "Apple", "Mango"];
2var 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:

1var fruits = ["Banana", "Orange", "Apple", "Mango"];
2fruits.push("Kiwi"); // Adds a new element ("Kiwi") to fruits

The push() method returns the new array length:

JavaScript Code:

1var fruits = ["Banana", "Orange", "Apple", "Mango"];
2var 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:

1var fruits = ["Banana", "Orange", "Apple", "Mango"];
2fruits.shift(); // Removes the first element "Banana" from fruits

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

JavaScript Code:

1var fruits = ["Banana", "Orange", "Apple", "Mango"];
2var 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:

1var fruits = ["Banana", "Orange", "Apple", "Mango"];
2fruits.unshift("Lemon"); // Adds a new element "Lemon" to fruits

The unshift() method returns the new array length.

JavaScript Code:

1var fruits = ["Banana", "Orange", "Apple", "Mango"];
2fruits.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:

1var fruits = ["Banana", "Orange", "Apple", "Mango"];
2fruits[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:

1var fruits = ["Banana", "Orange", "Apple", "Mango"];
2fruits[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:

1var fruits = ["Banana", "Orange", "Apple", "Mango"];
2delete 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:

1var fruits = ["Banana", "Orange", "Apple", "Mango"];
2fruits.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:

1var fruits = ["Banana", "Orange", "Apple", "Mango"];
2fruits.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:

1var fruits = ["Banana", "Orange", "Apple", "Mango"];
2fruits.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)

1var myGirls = ["Cecilie", "Lone"];
2var myBoys = ["Emil", "Tobias", "Linus"];
3var 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)

1var arr1 = ["Cecilie", "Lone"];
2var arr2 = ["Emil", "Tobias", "Linus"];
3var arr3 = ["Robin", "Morgan"];
4var 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)

1var arr1 = ["Emil", "Tobias", "Linus"];
2var 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:

1var fruits = ["Banana", "Orange", "Lemon", "Apple", "Mango"];
2var 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"):

1var fruits = ["Banana", "Orange", "Lemon", "Apple", "Mango"];
2var 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:

1var fruits = ["Banana", "Orange", "Lemon", "Apple", "Mango"];
2var citrus = fruits.slice(1, 3);

If the end argument is omitted, the slice() method slices out the rest of the array.

JavaScript Code:

1var fruits = ["Banana", "Orange", "Lemon", "Apple", "Mango"];
2var 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:

1var fruits = ["Banana", "Orange", "Apple", "Mango"];
2document.getElementById("demo").innerHTML = fruits.toString();

JavaScript Code:

1var fruits = ["Banana", "Orange", "Apple", "Mango"];
2document.getElementById("demo").innerHTML = fruits;

All JavaScript objects have a toString() method.

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