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Working with Arrays in JavaScript for beginners - Adding values

joelynn94 profile image Joseph Lynn Updated on ・3 min read

I recently finished (May 2020) the coding bootcamp I started back in October 2019. Now I am going back through materials to make sure I understand the fundamentals. I will be showing you a couple ways to add values to arrays. Here is my attempt to show you how to work with basic arrays.

Adding array values (basic)

Let's start by creating an empty array.

let newArray = [];

Next let's add a couple values to the array.
We will do that by specifying a new index of the array and adding a value

// declare the array and the location (index) you want to add a new value
// (remember: arrays index start at 0 - so index[0] is the first value)

// here we are adding 'Hello" to the first index [0]
newArray[0] = 'Hello';
// here we are adding 'World' to the second index [1]
newArray[1] = 'World';

console.log(newArray);
// Our results? The newArray now looks like this
[ 'Hello', 'World' ]

Adding values the to the end of an array (basic)

The push method allows you to add (push) values into an array.

// using the push method - we are adding another index to the array
// with the value 'New value':
newArray.push('New value');

console.log(newArray);
// 'New' gets added to the end of the array 
[ 'Hello', 'World', 'New value' ]

Adding values to the beginning of an array (basic)

The unshift method allows you to add values at the beginning of an array

// using the unshift method - we are adding another index to the array.
newArray.unshift('Beginning');

// unshift adds the new value to the beginning of the array 
// and moves the existing array values to new indexes
console.log(newArray);
// now our array looks like 
[ 'Beginning', 'Hello', 'World', 'New value' ]

Adding values to an array by creating a new array using concat

The concat method allows you to add values to an array. But unlike the push and unshift methods - this will create a brand new array.

// declare a new variable and set the new variable equal to
// the the old array with the value you want to add 
// Ex. syntax - array.concat(value)
let brandNewArray = newArray.concat('Newest Addition');

// you can see the value we added is at the end of the array 
console.log(brandNewArray);
// our brandNewArray values are 
[ 'Beginning', 'Hello', 'World', 'New value', 'Newest Addition' ]


console.log(newArray);
// and our newArray values are still 
[ 'Beginning', 'Hello', 'World', 'New value' ]

Adding values using splice

The splice method can be used for adding, removing or replacing values from an array. Using this method is a little more difficult than the last ones I have shown you. We will be using the brandNewArray from the last example.

First you need to indicate the index you want to make changes at. In our case I started at index 3.

// starting values 
console.log(brandNewArray);
[ 'Beginning', 'Hello', 'World', 'New value', 'Newest Addition' ]

// if you run this - by default the value at the index you specified
// and anything after it, will get deleted
brandNewArray.splice(3);

// that will delete the value at index 3 and everything after index 3
console.log(brandNewArray);
[ 'Beginning', 'Hello', 'World' ]

Then you add how many values you want to delete. In our case I don't want to delete anything - so we will indicate that by adding (, 0).

// starting values 
console.log(brandNewArray);
[ 'Beginning', 'Hello', 'World', 'New value', 'Newest Addition' ]

// if you run this - by adding the 0 as the second argument, your array will not change,
// because you are stating you do not want to delete anything
brandNewArray.splice(3, 0);

// after using splice
console.log(brandNewArray);
[ 'Beginning', 'Hello', 'World', 'New value', 'Newest Addition' ]

Now we want to add a value to this array. The value will be added at the 3rd index of the array and won't remove any values from the array

// starting values 
console.log(brandNewArray);
[ 'Beginning', 'Hello', 'World', 'New value', 'Newest Addition' ]

// now we are adding 'splice addition' to our array 
brandNewArray.splice(3, 0, 'splice addition');

// the results 
console.log(brandNewArray);
// this added 'splice addition' at the index we wanted to start at 
// and shifted the rest of the array indexes by 1
[ 'Beginning', 'Hello', 'World', 'splice addition', 'New value', 'Newest Addition' ]

And that's it. These are basic ways to add values to arrays. My next post will be showing you how to remove items from arrays.

Thanks for reading!

Posted on May 16 by:

joelynn94 profile

Joseph Lynn

@joelynn94

A bootcamp grad from Case Western University looking for a Developer position

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