Working with JavaScript's Array.concat() Method

In JavaScript, the Array.concat() method is a powerful tool introduced in ES6 (ECMAScript 6) used to merge two or more arrays. It comes handy in various programming scenarios where developers need to combine different datasets.

The Array.concat() method does not alter the original arrays. Instead, it returns a new array that consists of the content of the initial array followed by the content of each parameter array or value.

Here is a functional example:

let array1 = ['a', 'b', 'c'];
let array2 = ['d', 'e', 'f'];
let mergedArray = array1.concat(array2);
console.log(mergedArray);  // Output: ['a', 'b', 'c', 'd', 'e', 'f']

In the above code, array1 and array2 were not changed, and a new array (mergedArray) was created by combining array1 and array2.

The Array.concat() method can also take values as arguments, which are added at the end of the array.

let array1 = ['a', 'b', 'c'];
let mergedArray = array1.concat('d', 'e', 'f');
console.log(mergedArray);  // Output: ['a', 'b', 'c', 'd', 'e', 'f']

In JavaScript programming, best practices recommend ensuring that arrays (or any objects) are not mutated unless necessary. Hence, the use of Array.concat() which does not mutate the original arrays.

Remember, methods such as Array.join(), Array.merge(), and Array.combine() do not exist or have different functionalities in JavaScript. For instance, Array.join() is used to join all elements of an array into a string.

Understanding array methods like Array.concat(), can greatly simplify your code, make it more readable, and enhance your capabilities as a JavaScript developer.