Strategy Pattern

Real world example

Consider the example of sorting, we implemented bubble sort but the data started to grow and bubble sort started getting very slow. In order to tackle this we implemented Quick sort. But now although the quick sort algorithm was doing better for large datasets, it was very slow for smaller datasets. In order to handle this we implemented a strategy where for small datasets, bubble sort will be used and for larger, quick sort.

In plain words

Strategy pattern allows you to switch the algorithm or strategy based upon the situation.

Wikipedia says

In computer programming, the strategy pattern (also known as the policy pattern) is a behavioural software design pattern that enables an algorithm's behavior to be selected at runtime.

Programmatic example

Translating our example from above, we can easily implement this strategy in javascript using its feature of first class functions.

const bubbleSort = dataset => {
    console.log('Sorting with bubble sort')
    // ...
    // ...
    return dataset
}

const quickSort = dataset => {
    console.log('Sorting with quick sort')
    // ...
    // ...
    return dataset
}

And then we have our client that is going to use any strategy

const sorter = dataset => {
    if(dataset.length > 5){
        return quickSort
    } else {
        return bubbleSort
    }
}

And it can be used as

const longDataSet = [1, 5, 4, 3, 2, 8]
const shortDataSet = [1, 5, 4]

const sorter1 = sorter(longDataSet)
const sorter2 = sorter(shortDataSet)

sorter1(longDataSet) // Output : Sorting with quick sort
sorter2(shortDataSet) // Output : Sorting with bubble sort