Today I learned more about the distinction between declarative and imperative programming. I have seen the terms used in various places, but I could not give a good explanation about what they mean. So with a bit of curiosity and I thought that I would get a better handle on the definition.
Imperative programming is like how you do something, and declarative programming is more like what you do.
To me the above definition outlines the difference between the two paradigms, but it needs a good example to really understand what that means.
Modern JavaScript has a lot of nice features that can illustrate the difference. Let’s take a simple idea - add up an array of numbers and output the answer. That could be written two ways:
Imperatively
function add(array) {
let result = 0;
for (let i = 0; i < array.length; i++) {
result = result + array[i];
}
return result
}
console.log(add([1,2,3]));
// Output: 6
The code above is imperative. It tells you how it is going to execute. It takes an array, sets a result variable, loops over the array and adds the values, and eventually it outputs the result. There is nothing wrong with this code in my opinion. But you can imagine a more complex function might end up with a lot of LOC that could affect maintainability and readability.
Declaratively
function add(array) {
return array.reduce((prev, current) => prev + current, 0);
}
console.log(add([1,2,3]));
// Output: 6
The declarative example is interesting. It requires a bit more knowledge about native JavaScript array methods, namely the use of reduce (which I only began to use fairly recently). reduce is an abstraction, as in it does some work for you under the hood. It allows the add function to be written in one LOC. It tells you what it is going to execute. But it does take that slight advanced knowledge, and to me is only more readable once you understand what reduce does.
Summary
I now have a better idea about what the two terms mean. I am going to use this knowledge and reflect upon the code I write and how it can be improved by making it more declarative.