When working with arrays in JavaScript, it’s common to need to merge or extend them with new values. Modern JavaScript provides several ways to accomplish this, each with its own advantages depending on readability, mutability, and style preferences. The following examples illustrate different approaches using an existing array named sharedValueNotAllowedBL and another array called businessLinesToBeRemove.
One of the most popular techniques is the spread operator. By writing:
sharedValueNotAllowedBL = [
...sharedValueNotAllowedBL,
...businessLinesToBeRemove
];
you create a new array that includes all elements from both arrays. This approach is concise, readable, and avoids mutating the original arrays directly.
Another option is to nest one of the arrays inside the spread expression:
[...sharedValueNotAllowedBL, businessLinesToBeRemove]
In this case, the second array is inserted as a single element rather than being expanded. The result is an array whose last item is itself an array, which may or may not be the intended structure. This approach is useful only when you specifically need to keep the second array intact as a separate element.
A more traditional method for combining arrays is the concat function:
sharedValueNotAllowedBL.concat(businessLinesToBeRemove)
The concat method returns a new array containing the elements of the first array followed by those of the second. Like the spread operator, it does not modify the original arrays. This method is still widely used and may feel more explicit, especially for developers who prefer a functional style or who work in environments where spread syntax is less common.
All of these techniques can be valid depending on your requirements. The spread operator offers modern, flexible syntax and is ideal for cloning and merging. The nested spread example is helpful when you need to preserve an array as a single item. The concat method remains a clear and reliable choice for building new arrays without mutation. Understanding these options allows you to choose the most appropriate pattern for maintaining clean, predictable, and expressive JavaScript code.