Let’s say you have two arrays and want to merge them:

const firstTeam = ['Olivia', 'Emma', 'Mia']
const secondTeam = ['Oliver', 'Liam', 'Noah']

One way to merge two arrays is to use concat() to concatenate the two arrays:

const total = firstTeam.concat(secondTeam)

But since the 2015 Edition of the ECMAScript now you can also use spread to unpack the arrays into a new array:

const total = [...firstTeam, ...secondTeam]
console.log(total)

The result would be:

// ['Olivia', 'Emma', 'Mia', 'Oliver', 'Liam', 'Noah']

There is also another way, in case you don't want to create a new array but modify one of the existing arrays:

firstTeam.push(...secondTeam);
firstTeam; // ['Olivia', 'Emma', 'Mia', 'Oliver', 'Liam', 'Noah']