In this article we are looking at how to use the concept of Arrays in Javascript ES6. this article is a part of series – Learn Javascript ES6
If you are familiar with Javascript ES6, then you might find some useful tricks to use arrays in this article.
There are 3 methods to concatenate arrays using Javascript :
Method 1: using Spread Operator (…)
Assume you have two arrays of numbers, and you want to join the two arrays :
const array1 = [1,2,3];
const array2 = [3,4,5];
// join the two arrays using spread operater '...'
const resultArray = [...array1, ...array2]
console.log(resultArray);
// O/P : [1,2,3,3,4,5]
Don’t forget, one can do this too:
const array1 = [1,2,3];
const array2 = [...array1, 4];
console.log(array2);
// O/P : [1,2,3,4]
Now what if we want to concatenate three arrays ?
const array1 = [1,2,3]
const array2 = [4,5,6]
const array3 = [7,8,9]
const resultArray = [...array1, ...array2, ...array3];
console.log(resultArray);
// O/P : [1, 2, 3, 4, 5, 6, 7, 8, 9]
Now what will happen if we try to concatenate two different arrays with different data types ?
let array1 = "letters";
let array2 = [1, 2, 3, 4];
let resultArray = [...array1, ...array2];
console.log(resultArray );
// O/P: ["l", "e", "t", "t", "e", "r", "s", 1, 2, 3, 4]
But why ? why not [“letters”, 1, 2, 3 ,4]. This happens because if we use spread our string, it will split the word in to seperate letters. You can probably use the method 2 for that.
Lets now see on how we can do concat operation using array objects :
const array1 = [
{
"id": 1,
"name": "John",
},
{
"id": 2,
"name": "Ron"
}
];
const array2 = [
{
"id": 3,
"name": "Harry",
},
{
"id": 4,
"name": "Hermione"
}
]
const resultArray = [...array1, ...array2];
console.log(resultArray);
Method 2: Using Array.prototype.concat()
Let’s use the same example, but this time using concat() method. This method does not change the existing arrays, but instead returns a new array.
const array1 = [1,2,3];
const array2 = [3,4,5];
// join the two arrays using concat()
const resultArray = array1.concat(array2);
console.log(resultArray);
// O/P : [1, 2, 3, 3, 4, 5]
But what If we want to concatenate three arrays ?
const array1 = [1,2,3];
const array2 = [4,5,6];
const array3 = [7,8,9];
const resultArray = array1.concat(array2, array3);
console.log(resultArray);
// O/P : [1,2,3,4,5,6,7,8,9]
now let’s check for concatenating arrays of two different types:
const array1 = [1,2,3,4];
const array2 = 'letters';
const resultArray = array1.concat(array2);
console.log(resultArray);
// O/P : [1, 2, 3, 4, "letters"]
Method 3: using Array.prototype.push()
when using push, its important to remember that it won’t create a new array, and change existing array data. so use this by keeping this in mind.
Using Spread and push()
const array1 = [1,2,3];
const array2 = [4,5,6];
const resultArray = array1.push(...array2);
// when you use push, it returns the LENGTH of the combined array
console.log(resultArray); // 6
console.log(array1); // [1, 2, 3, 4, 5, 6]
console.log(array2); // [4, 5, 6]
Using forEach and push() :
const array1 = [1,2,3];
const array2 = [4,5,6];
const resultArray = array2.forEach(item => array1.push(item));
console.log(array1); // [1,2,3,4,5,6]
Using for and push() :
const array1 = [1,2,3];
const array2 = [4,5,6];
for(let x=0; x<array2.length; x++) {
array1.push(array2[x]);
}
console.log(array1); // 1,2,3,4,5,6
Using apply() with push :
We can use push.apply(arr, otherArray) to append two arrays to an existing array. In this case the first “array” will be having the appended array.
const array = ['a', 'b'];
const elements = [0, 1, 2];
array.push.apply(array, elements);
console.info(array); // ["a", "b", 0, 1, 2]Zipper Merge ( Merging two sorted arrays )
Let’s think of a scenario, where we have two arrays (both sorted) like :
const array1 = [1, 3, 5];
const array2 = [2, 4, 6];
and the output we want is also sorted ! something like :
const resultArray = [1, 2, 3, 4, 5, 6];
This can be solved easily using spread operator :
// function to return zipped array
function zip(array1, array2) {
// merge the two sorted arrays
let result = [...array1, ...array2]; // [1, 3, 5, 2, 4, 6]
// sort the result array again
return result.sort((a,b) => a-b); // [1, 2, 3, 4, 5, 6]
}
const array1 = [1, 3, 5];
const array2 = [2, 4, 6];
const resultArray = zip(array1, array2);
console.log(resultArray); // [1, 2, 3, 4, 5, 6]
Unique Array from Two Arrays
Now let’s think of a scenario, where you have two arrays (with some elements in common ) like:
const array1 = [1, 2, 3, 4];
const array2 = [3, 4, 5, 6];
and the output we want is a new array with unique elements only :
const resultArray = [1, 2, 3, 4, 5, 6];
So what should we do ? We can create a unique array using spread operator and sets like this:
const array1 = [1, 2, 3, 4];
const array2 = [3, 4, 5, 6];
const mergedArray = [...array1, ...array2];
console.log(mergedArray) // [1, 2, 3, 4, 3, 4, 5, 6]
const resultArray = [...new Set(mergedArray)];
console.log(resultArray) // [1, 2, 3, 4, 5, 6]
Thats all for today, for more tutorials, follow our series – Learn Javascript ES6
