Quick Tip - Array.prototype.concat()

Hello everyone, I’m back, this time with a quick tip about how to use the concat() method to merge arrays in JavaScript, so no time to waste, let’s get started.

The concat() method is used to merge one array with another array or element passed as parameter. As others JavaScript methods,concat() don’t change the original array, but instead returns a new array with all the changes. Let’s see a example:

const firstList = [1,2,3];
const secondList = [4,5,6];

const result = firstList.concat(secondList);
//The result will be equal to [1,2,3,4,5,6]

If you pass two or more diferents arrays as parameter to concat(), this will works to and the elements will be add in the new array, following the order of the parameters.

const firstArray = [1];
const secondArray = [2,3,4];
const thirdArray = [5,6];

const result = firstArray.concat(secondArray, thirdArray);
//The result will be equal to [1,2,3,4,5,6]

We can pass too, single values or more complex elements like objects and these elements don’t need to be of the same type, we can concat a array of numbers with strings, there’s no problem.

const firstArray = [1];
const secondArray = [2,3,4];

const stringNumber = "5";

const objectTest = {"name": "Batman", "super_power": "Money"};

const result = firstArray.concat(secondArray, stringNumber, objectTest);
//The result will be equal to [1,2,3,4,"5",{"name": "Batman", "super_power": "Money"}]

And for last, we can merge nested arrays, like this:

const firstArray = [[1]]
const secondArray = [2, 3]
const thirdArray = [4, [5,6,7]]

const result = firstArray.concat(secondArray, thirdArray);
//The result will be equal to [[1], 2, 3, 4, [5,6,7]]

We can add a new value to one of the nested arrays, like this:

result[0].push("0"); 
//The result will be equal to [[1, "0"], 2, 3, 4, [5,6,7]]

So, this is all for now folks, thanks for reading and for more posts you can check my personal blog hallessandro.github.io.