How to Remove Elements From a JavaScript Array Safely

How to Remove Elements From a JavaScript Array Safely

In this post, we will learn 9 Ways to Remove Elements From A JavaScript Array, plus How to Safely Clear JavaScript Arrays

JavaScript arrays allow you to group values and iterate over them. You can add and remove array elements in different ways. Unfortunately there is not a simple Array.remove method.

So, how do you delete an element from a JavaScript array?

Instead of a delete method, the JavaScript array has a variety of ways you can clean array values.

You can remove elements from the end of an array using pop, from the beginning using shift, or from the middle using splice. The JavaScript Array filter method to create a new array with desired items, a more advanced way to remove unwanted elements.

  • Removing Elements from End of a JavaScript Array
  • Removing Elements from Beginning of a JavaScript Array
  • Using Splice to Remove Array Elements
  • Removing Array Items By Value Using Splice
  • The Lodash Array Remove Method
  • Making a Remove Method
  • Explicitly Remove Array Elements Using the Delete Operator
  • Clear or Reset a JavaScript Array
  • Summary

There are different methods and techniques you can use to remove elements from JavaScript arrays:

  • pop - Removes from the End of an Array
  • shift - Removes from the beginning of an Array
  • splice - removes from a specific Array index
  • filter - allows you to programatically remove elements from an Array
Removing Elements from End of a JavaScript Array

JavaScript Array elements can be removed from the end of an array by setting the length property to a value less than the current value. Any element whose index is greater than or equal to the new length will be removed.


var ar = [1, 2, 3, 4, 5, 6];
ar.length = 4; // set length to remove elements
console.log( ar ); //  [1, 2, 3, 4]

The pop method removes the last element of the array, returns that element, and updates the length property. The pop method modifies the array on which it is invoked, This means unlike using delete the last element is removed completely and the array length reduced.


var ar = [1, 2, 3, 4, 5, 6];
ar.pop(); // returns 6
console.log( ar ); // [1, 2, 3, 4, 5]
Removing Elements from Beginning of a JavaScript Array

How do you remove the first element of a JavaScript array?

The shift method works much like the pop method except it removes the first element of a JavaScript array instead of the last.

There are no parameters since the shift method only removed the first array element. When the element is removed the remaining elements are shifted down.


var ar = ['zero', 'one', 'two', 'three'];
ar.shift(); // returns "zero"
console.log( ar ); // ["one", "two", "three"]

The shift method returns the element that has been removed, updates the indexes of remaining elements, and updates the length property. It modifies the array on which it is invoked.

If there are no elements, or the array length is 0, the method returns undefined.

Using Splice to Remove Array Elements in JavaScript

The splice method can be used to add or remove elements from an array. The first argument specifies the location at which to begin adding or removing elements. The second argument specifies the number of elements to remove. The third and subsequent arguments are optional; they specify elements to be added to the array.

Here we use the splice method to remove two elements starting from position three (zero based index):


var arr = [1, 2, 3, 4, 5, 6, 7, 8, 9, 0];
var removed = arr.splice(2,2);

/*
removed === [3, 4]
arr === [1, 2, 5, 6, 7, 8, 9, 0]
*/

An array containing the removed elements is returned by the splice method. You can see the removed array contains [3, 4] and the original array contains the remaining values.

The splice method can also be used to remove a range of elements from an array.


["bar", "baz", "foo", "qux"]

list.splice(0, 2) 
// Starting at index position 0, remove two elements ["bar", "baz"] and retains ["foo", "qux"].
Removing Array Items By Value Using Splice

If you know the value you want to remove from an array you can use the splice method. First you must identify the index of the target item. You then use the index as the start element and remove just one element.


var arr = [1, 2, 3, 4, 5, 6, 7, 8, 9, 0];

for( var i = 0; i < arr.length; i++){ 
   if ( arr[i] === 5) {
     arr.splice(i, 1); 
   }
}

//=> [1, 2, 3, 4, 6, 7, 8, 9, 0]

This is a simple example where the elements are integers. If you have an array of objects you would need a more sophisticated routine.

This works if you only want to remove a single item. If you want to remove multiple items that match your criteria there is a glitch.

As the items are removed from the array the index still increments and the next item after your matched value is skipped.

The simple solution is to modify the above example to decrement the index variable so it does not skip the next item in the array.


var arr = [1, 2, 3, 4, 5, 5, 6, 7, 8, 5, 9, 0];

for( var i = 0; i < arr.length; i++){ 
   if ( arr[i] === 5) {
     arr.splice(i, 1); 
     i--;
   }
}

//=> [1, 2, 3, 4, 6, 7, 8, 9, 0]

In the modified example I added 2 additional 5 values to the array. I also added 'i--;' after the splice call.

Now when you execute the loop it will remove every matching item.

Using the Array filter Method to Remove Items By Value

Unlike the splice method, filter creates a new array. filter() does not mutate the array on which it is called, but returns a new array.

filter() has a single parameter, a callback method. The callback is triggered as the filter method iterates through the array elements. It will pass three values to the callback: the current value or element, the current array index and the full array.

The callback method should return either true or false. It is your responsibility to test the value (element) to see if it meets your criteria. If it does you can return true. Elements that return true are added to the new, filtered array.


var array = [1, 2, 3, 4, 5, 6, 7, 8, 9, 0];

var filtered = array.filter(function(value, index, arr){

    return value > 5;

});

//filtered => [6, 7, 8, 9]
//array => [1, 2, 3, 4, 5, 6, 7, 8, 9, 0]

You should note a new array containing matching values is returned. The original array is left untouched. I find this useful because I often want to retain an original data source, but retrieve subsets based on different logic sets.

The Lodash Array Remove Method

Sometimes utility libraries are the best way to solve more complex problems. Lodash provides a rich set of array manipulation methods, one being remove.

The Lodash remove method works much like the array filter method, but sort of in reverse. It does not save the original array values, but removes matching elements. It returns the matching elements as a new array.


var array = [1, 2, 3, 4];
var evens = _.remove(array, function(n) {
  return n % 2 === 0;
});

console.log(array);
// => [1, 3]

console.log(evens);
// => [2, 4]
Making a Remove Method

As I mentionmed before, there is no native Array.remove method. The Lodash method does solve this problem, but you may not always want to use Lodash. This does not mean you cannot create a utility method. John Resig gave us a model to follow, however he extended the Array prototype, which is a bad idea.

Instead I created an Array remove utility method that can be added to a helper or utility library. Like the Lodash remove method the first parameter is the target array. It uses Array.filter to return elements not matching a value.


function arrayRemove(arr, value) {

   return arr.filter(function(ele){
       return ele != value;
   });

}

var result = arrayRemove(array, 6);

// result = [1, 2, 3, 4, 5, 7, 8, 9, 0]
Explicitly Remove Array Elements Using the Delete Operator

You can remove specific array elements using the delete operator:


var ar = [1, 2, 3, 4, 5, 6];
delete ar[4]; // delete element with index 4
console.log( ar ); // [1, 2, 3, 4, undefined, 6]
alert( ar ); // 1,2,3,4,,6

Using the delete operator does not affect the length property. Nor does it affect the indexes of subsequent elements. The array becomes sparse, which is a fancy way of saying the deleted item is not removed but becomes undefined. Compare using delete with the splice method described below.

The delete operator is designed to remove properties from JavaScript objects, which arrays are objects.

The reason the element is not actually removed from the array is the delete operator is more about freeing memory than deleting an element. The memory is freed when there are no more references to the value.

Clear or Reset a JavaScript Array

What if you want to empty an entire array and just dump all of it's elements?

There are a couple of techniques you can use to create an empty or new array.

The simplest and fastest technique is to set an array variable to an empty array:



var ar = [1, 2, 3, 4, 5, 6];

//do stuff

ar = [];

//a new, empty array!

The problem this can create is when you have references to the variable. The references to this variable will not change, they will still hold the original array's values. This of course can create a bugπŸ›.

This is an over simplified example of this scenario:



var arr1 = [1, 2, 3, 4, 5, 6];

var arr2 = arr1;  // Reference arr1 by another variable 

arr1 = [];

console.log(arr2); // Output [1, 2, 3, 4, 5, 6]

A simple trick to clear an array is to set its length property to 0.



var ar = [1, 2, 3, 4, 5, 6];

console.log(ar); // Output [1, 2, 3, 4, 5, 6]

ar.length = 0;

console.log(ar); // Output []

Another, sort of unnatural technique, is to use the splice method, passing the array length as the 2nd parameter. This will return a copy of the original elements, which may be handy for your scenario.



var ar = [1, 2, 3, 4, 5, 6];

console.log(ar); // Output [1, 2, 3, 4, 5, 6]

ar.splice(0, ar.length);

console.log(ar); // Output []

The last two techniques don't create a new array, but change the array's elements. This means references should also update.

There is another way, using a while loop. It feels a little odd to me, but at the same time looks fancy, so it may impress some friends!



var ar = [1, 2, 3, 4, 5, 6];

console.log(ar); // Output [1, 2, 3, 4, 5, 6]

  while (ar.length) {
    ar.pop();
  }

console.log(ar); // Output []

Not a way I would go about clearing a JavaScript array, but it works and it is readable. Some performance test have also shown this to be the fastest technique, so maybe it is better than I originally thought!

Summary

Removing JavaScript Array items is important to managing your data. There is not a single 'remove' method available, but there are different methods and techniques you can use to purge unwanted array items.

This article has reviewed these methods and how they can be used. You also saw how to create a helper method that makes removing items from an array a bit easier and consistent.

Thank you for reading !

JavaScript: Remove Element from an Array

JavaScript: Remove Element from an Array

Here we will explain how to remove the last element from array javascript, remove the first element from array javascript, remove specific elements from array javascript with different techniques and examples.Remove element or object from an array in javascript.

Remove element or object from an array in javascript. Here we will explain how to remove the last element from array javascript, remove the first element from array javascript, remove specific elements from array javascript with different techniques and examples.

This tutorial demonstrates different techniques and methods with examples to removing the first, last or specific index elements from an array in javascript.

javaScript Methods: To Remove Element From Array javaScript

This tutorial demonstrates an easy way for you. To remove the first, last specific index element from array in javascript:

1. First Method – Array Shift() JavaScript

Use the javascript array shift() method, which is used to remove the first element of the array javascript.

Let’s take an example to remove the first element from an array javascript using array shift method:

 var array = ["bar",Β "baz",Β "foo",Β "qux"];
 array.shift();
 
 console.log( array );

Result of the above example:

After removed the first element from an array using javascript shift method. The output will look like:

["baz", "foo", "qux"]

2. Second Method:- Array pop() javascript

Using the javaScript pop method, which is used to remove the last element of the array javascript, returns that new element array.

 var arr = ["bar",Β "baz",Β "foo",Β "qux"];
 
arr.pop();
 
console.log( arr );

Result of the above example

After removed the last element from an array using javascript pop method. The output will look like:

["bar", "baz", "foo"]

3. Third Method:- Array splice() javascript

Use the javascript splice() method, that is used to add or remove element or item from an array javascript.

Let’s take an example to remove specific index elements from array javascript. In this example, we will remove 1 to 2 index values from the array.

If you want to want to know more about javascript Array Splice Method, Read Here

  var arr = ["bar", "baz", "foo", "qux"];

  arr.splice(1, 2);

  console.log(arr);

Result of the above example

["bar", "qux"]

If you want to know more about javascript array methods, you may like

JavaScript Array.flatMap()

JavaScript Array.flatMap()

JavaScript Array.flatMap(): Use flatMap to map over an array and flatten the result array in one go! Now lets up the game and introduce "flatMap". It combines the steps of first mapping over the array with `map()` & then calling `flat()`. Instead of calling 2 methods, just use `flatMap()` πŸ‘

Now lets up the game and introduce "flatMap". It combines the steps of first mapping over the array with map() & then calling flat(). Instead of calling 2 methods, just use flatMap() πŸ‘

const foods = ['🍫', '🍦'];

// ❌ map + flat
foods.map(food => [food, 'πŸ˜‹']).flat();

// βœ… flatMap
foods.flatMap(food => [food, 'πŸ˜‹']);

// Result
// ['🍫', 'πŸ˜‹', '🍦', 'πŸ˜‹']

How flatMap() works?

Let's go through step-by-step what flatMap() is doing. I was a bit confused when I first learned this one. Cause I thought it flattens and then it does the mapping. But no πŸ™…. It first map() and then it flat().

const names = ['jane', 'john'];

// Step 1: map
const nestedArray = names.map((name, index) => [name, index]);
// [ ['jane', 1], ['john', 2 ] ]

So now we have a nested array. And we can use flat() to flatten the array.

const nestedArray = [
  ['jane', 1],
  ['john', 2]
];

nestedArray.flat();
// [ 'jane', 1, 'john', 2 ]

Of course, we can shorten this and just call flatMap(). Let's take a look πŸ‘€

const names = ['jane', 'john'];

const result = names.flatMap((name, index) => [name, index]);

// [ 'jane', 1, 'john', 2 ]

And Voila! We have the same result πŸ‘

flatMap only flattens 1-level deep

With flat(), it accepts a parameter where you set the depth. What this means is you can specify how deep a nested array should be flattened.

const depth1 = [[1], [2]];
depth1.flat(); // same as depth.flat(1)
// [1, 2]

const depth2 = [[[1, 2]]];
depth2.flat(2);
// [1, 2]

Now for flatMap(), you can only go 1-level deep.

const names = ['jane'];

names.flatMap((name, index) => [[name, index]]);
//  [ ['jane', 1] ]

Let's break this into 2 steps, so you can see what's going on.

const names = ['jane'];

// Step 1: created a 2-level deep array
const twoLevelDeep = names.map((name, index) => [[name, index]]);
// [ [ ['jane', 1] ] ]

// Step 2: flat using depth 1
twoLevelDeep.flat();
//  [ ['jane', 1] ]

But if you do it separately, I can pass a depth parameter and flatten it completely:

twoLevelDeep.flat(2);
// [ 'jane', 0, 'john', 1 ]

So, if you want it to flatten beyond depth of 1. Then it is better to NOT use flatMap() and just call the methods separately πŸ‘

flatMap to filter item

One really cool you can do with flatMap is to remove an element. In this example, I want to remove all negative numbers.

const numbers = [1, 2, -3, -4, 5];

numbers.flatMap(number => {
  return number < 0 ? [] : [number];
});

// [ 1, 2, 5]

That's really cool! It's like acting like a filter. But how is this actually working. The secret is the empty array. Let's see what I mean.

const emptyNestedArray = [[], 1];

emptyNestedArray.flat();
// [ 1 ]

When you try to flatten an element that's an empty array, it simply removes that item. So we can use that knowledge to make flatMap act kind of like filter method. Neat right! πŸ‘

Resources

Originally published at https://www.samanthaming.com

JavaScript array : How to merge two arrays in JavaScript

JavaScript array : How to merge two arrays in JavaScript

In this post, We go over how to merge two arrays in JavaScript using the concat method and the spread syntax.

Array Concat() method

The concat method is used to merge two arrays. As a result, it returns a new array instead of modifying the existing array.

Let’s look at an example using the concat method. We have two arrays named fruits1 and fruits2. They both contain strings that correspond to a fruit.

const fruits1 = ['apple', 'banana', 'grapes'];
const fruits2 = ['melons', 'watermelon'];

const combinedFruits = fruits1.concat(fruits2);

console.log(combinedFruits); //[ 'apple', 'banana', 'grapes', 'melons', 'watermelon' ]


Array Spread syntax

Now let’s look at an example using the spread syntax.


const fruits1 = ['apple', 'banana', 'grapes'];
const fruits2 = ['melons', 'watermelon'];

const combinedFruits = [...fruits1, ...fruits2];

console.log(combinedFruits); //[ 'apple', 'banana', 'grapes', 'melons', 'watermelon' ]

In this example, we created a new array and assigned it to the variable combinedFruits. We then took the two fruits array and used the spread them out in the array. We used the ... syntax to spread out the contents of the fruits array into the new array.

Thanks for reading !