JavaScript — Prerequisites for Functional Programming: Declarative Code
An article for Mid level JavaScript Developers.
This is part of a series “JavaScript — Prerequisites for Functional Programming”
Functional Programming is the process of building software by following a certain rules. One of which is discussed in this article.
Use Declarative (what) rather than imperative code (how)
Imperative Programming involves typing lines of code describing how a result is achieved.
A statement (
Imperative code) is a piece of code which performs some action. Examples of commonly used statements includefor,if,switch,throw, etc…
const doubleMap = numbers => {
const doubled = [];
for (let i = 0; i < numbers.length; i++) {
doubled.push(numbers[i] * 2);
}
return doubled;
};
console.log(doubleMap([2, 3, 4])); // [4, 6, 8]Declarative Programmings involves describing desired results without explicitly listing steps that must be performed.
An expression (
Declarative code) is a piece of code which evaluates to some value. Expressions are usually some combination of function calls, values, and operators which are evaluated to produce the resulting value.
const doubleMap = numbers => numbers.map(n => n * 2);
console.log(doubleMap([2, 3, 4])); // [4, 6, 8]
