Functional programming is a programming paradigm that emphasizes the evaluation of functions. In functional programming, functions are considered first-class citizens, which means that they can be passed as arguments to other functions and returned from other functions.
In JavaScript, there are many ways to create functions. One way is to use the function keyword, as in:
function myFunction() {
// do something
}
Another way is to use the => (fat arrow) syntax, as in:
const myFunction = () => {
// do something
}
The => syntax is a shorthand for the function keyword. It is often used in place of the function keyword when creating anonymous functions, as in:
const myArray = [1, 2, 3, 4, 5];
myArray.map(x => x * 2); // [2, 4, 6, 8, 10]
In the example above, the myArray.map() method takes a function as an argument. The function passed to the map() method is an anonymous function that multiplies each element in the array by 2.
In addition to being passed as arguments to other functions, functions can also be returned from other functions. For example, the following function returns a function:
function createMultiplier(x) {
return y => y * x;
}
const multiplier = createMultiplier(2);
multiplier(5); // 10
In the example above, the createMultiplier() function takes a number as an argument and returns a function. The function that is returned takes a number as an argument and returns the result of multiplying the number by the number that was passed to the createMultiplier() function.
The ability to return functions from other functions is a powerful feature of functional programming. It allows for the creation of higher-order functions, which are functions that take other functions as arguments and/or return functions.
One of the most popular higher-order functions in functional programming is the map() function. The map() function takes a function as an argument and applies that function to each element in an array. For example:
const myArray = [1, 2, 3, 4, 5];
myArray.map(x => x * 2); // [2, 4, 6, 8, 10]
In the example above, the map() function takes an anonymous function as an argument. The anonymous function takes a number as an argument and returns the result of multiplying the number by 2. The map() function applies the anonymous function to each element in the myArray array and returns a new array with the results.
In addition to the map() function, there are many other higher-order functions in functional programming. Some of the other popular higher-order functions are:
functional programming is a programming paradigm that emphasizes the evaluation of functions. In functional programming, functions are considered first-class citizens, which means that they can be passed as arguments to other functions and returned from other functions.
In JavaScript, there are many ways to create functions. One way is to use the function keyword, as in:
function myFunction() {
// do something
}
Another way is to use the => (fat arrow) syntax, as in:
const myFunction = () => {
// do something
}
The => syntax is a shorthand for the function keyword. It is often used in place of the function keyword when creating anonymous functions, as in:
const myArray = [1, 2, 3, 4, 5];
myArray.map(x => x * 2); // [2, 4, 6, 8, 10]
In the example above, the myArray.map() method takes a function as an argument. The function passed to the map() method is an anonymous function that multiplies each element in the array by 2.
In addition to being passed as arguments to other functions, functions can also be returned from other functions. For example, the following function returns a function:
function createMultiplier(x) {
return y => y * x;
}
const multiplier = createMultiplier(2);
multiplier(5); // 10
In the example above, the createMultiplier() function takes a number as an argument and returns a function. The function that is returned takes a number as an argument and returns the result of multiplying the number by the number that was passed to the createMultiplier() function.
The ability to return functions from other functions is a powerful feature of functional programming. It allows for the creation of higher-order functions, which are functions that take other functions as arguments and/or return functions.
One of the most popular higher-order functions in functional programming is the map() function. The map() function takes a function as an argument and applies that function to each element in an array. For example:
const myArray = [1, 2, 3, 4, 5];
myArray.map(x => x * 2); // [2, 4, 6, 8, 10]
In the example above, the map() function takes an anonymous function as an argument. The anonymous function takes a number as an argument and returns the result of multiplying the number by 2. The map() function applies the anonymous function to each element in the myArray array and returns a new array with the results.
In addition to the map() function, there are many other higher-order functions in functional programming. Some of the other popular higher-order functions are:
The ability to pass functions as arguments and return functions from other functions is a powerful feature of functional programming. However, it can also be a source of confusion for developers who are new to the paradigm. In this post, we will take a look at a practical guide to using the Maybe monad in functional JavaScript.
What is a monad?
In the context of functional programming, a monad is a structure that allows for the composition of functions. Monads are often used to provide a way to chain together a series of functions. Each function in the chain takes a value as an input and returns a value as an output. The output of one function in the chain is then passed as the input to the next function in the chain.
Monads are a way to abstract away the details of how the functions in the chain are implemented. This allows for the functions in the chain to be easily swapped out and replaced with different functions.
What is the Maybe monad?
The Maybe monad is a monad that represents a value that may or may not be present. The Maybe monad is often used to deal with the possibility of null values.
In JavaScript, the Maybe monad can be implemented using the Maybe class from the folktale library.
const { Maybe } = require('folktale/maybe');
const myFunction = x =>
Maybe.of(x) // the "of" method creates a Maybe instance from a value
.map(x => x * 2) // the "map" method applies a function to the value
.getOrElse(null); // the "getOrElse" method returns the value or a default value if the value is not present
myFunction(10); // 20
myFunction(null); // null
In the example above, the myFunction() function takes a number as an argument and returns the result of multiplying the number by 2. If the number passed to the myFunction() function is null, then the function will return null.
The Maybe monad can be used to deal with the possibility of null values in a more elegant way than using the traditional if...else statement.
const myFunction = x =>
Maybe.of(x)
.map(x => x * 2)
.getOrElse(null);
myFunction(10); // 20
myFunction(null); // null
In the example above, the myFunction() function takes a number as an argument and returns the result of multiplying the number by 2. If the number passed to the myFunction() function is null, then the function will return null.
The Maybe monad can also be used to deal with the possibility of undefined values.
const myFunction = x =>
Maybe.of(x)
.map(x => x * 2)
.getOrElse(undefined);
myFunction(10); // 20
myFunction(undefined); // undefined
In the example above, the myFunction() function takes a number as an argument and returns the result of multiplying the number by 2. If the number passed to the myFunction() function is undefined, then the function will return undefined.
The Maybe monad can be used to safely access properties of an object that may or may not be present.
const myObject = {
a: 10,
b: 20
};
const myFunction = x =>
Maybe.of(myObject[x])
.map(x => x * 2)
.getOrElse(null);
myFunction('a'); // 20
myFunction('c'); // null
In the example above, the myFunction() function takes a property name as an argument and returns the value of the property multiplied by 2. If the property does not exist, then the function will return null.
The Maybe monad can also be used to call a function that may or may not be present.
const myObject = {
a: 10,
b: 20,
myFunction: x => x * 2
};
const myFunction = x =>
Maybe.of(myObject.myFunction)
.map(f => f(x))
.getOrElse(null);
myFunction(10); // 20
myFunction(); // null
In the example above, the myFunction() function takes a number as an argument and returns the result of calling the myObject.myFunction() function with the number. If the myObject.myFunction() function does not exist, then the myFunction() function will return null.
The Maybe monad can be used to deal with the possibility of error values.
const myFunction = x =>
Maybe.of(x)
.map(x => {
if (x === 0) {
throw new Error('x cannot be 0!');
}
return x * 2;
})
.getOrElse(null);
myFunction(10); // 20
myFunction(0); // null
In the example above, the myFunction() function takes a number as an argument and returns the result of multiplying the number by 2. If the number passed to the myFunction() function is 0, then the function will return null.
The Maybe monad can be used to deal with the possibility of values that are not of the expected type.
const myFunction = x =>
Maybe.of(x)
.map(x => {
if (typeof x !== 'number') {
throw new Error('x must be a number!');
}
return x * 2;
})
.getOrElse(null);
myFunction(10); // 20
myFunction('10'); // null
In the example above, the myFunction() function takes a value as an argument and returns the result of multiplying the value by 2. If the value passed to the myFunction() function is not a number, then the function will return null.
The Maybe monad can be used to deal with the possibility of values that are not of the expected type.
const myFunction = x =>
Maybe.of(x)
.map(x => {
if (typeof x !== 'number') {
throw new Error('x must be a number!');
}
return x * 2;
})
.getOrElse(null);
myFunction(10); // 20
myFunction('10'); // null
In the example above, the myFunction() function takes a value as an argument and returns the result of multiplying the value by 2. If the value passed to the myFunction() function is not a number, then the function will return null.
The Maybe monad can be used to compose a series of functions that may or may not return a value.
const myFunction = x =>
Maybe.of(x)
.map(x => x * 2)
.map(x => x + 1)
.map(x => x / 2)
.getOrElse(null);
myFunction(10); // 10.5
myFunction(null); // null
In the example above, the myFunction() function takes a number as an argument and returns the result of composing a series of functions. If any of the functions in the series return null, then the myFunction() function will also return null.
The Maybe monad can be used to safely access properties of an object that may or may not be present.
const myObject = {
a: 10,
b: 20
};
const myFunction = x =>
Maybe.of(myObject[x])
.map(x => x * 2)
.getOrElse(null);
myFunction('a'); // 20
myFunction('c'); // null
In the example above, the myFunction() function takes a property name as an argument and returns the value of the property multiplied by 2. If the property does not exist, then the function will return null.
The Maybe monad can also be used to call a function that may or may not be present.
const myObject = {
a: 10,
b: 20,
myFunction: x => x * 2
};
const myFunction = x =>
Maybe.of(myObject.myFunction)
.map(f => f(x))
.getOrElse(null);
myFunction(10); // 20
myFunction(); // null
In the example above, the myFunction() function takes a number as an argument and returns the result of calling the myObject.myFunction() function with the number. If the myObject.myFunction() function does not exist, then the myFunction() function will return null.
The Maybe monad can be used to deal with the possibility of error values.
const myFunction = x =>
Maybe.of(x)
.map(x => {
if (x === 0) {
throw new Error('x cannot be 0!');
}
return x * 2;
})
.getOrElse(null);
myFunction(10); // 20
myFunction(0); // null
In the example above, the myFunction() function takes a number as an argument and returns the result of multiplying the number by 2. If the number passed to the myFunction() function is 0, then the function will return null.
The Maybe monad can be used to deal with the possibility of values that are not of the expected type.
const myFunction = x =>
Maybe.of(x)
.map(x => {
if (typeof x !== 'number') {
throw new Error('x must be a number!');
}
return x * 2;
})
.getOrElse(null);
myFunction(10); // 20
myFunction('10'); // null
In the example above, the myFunction() function takes a value as an argument and returns the result of multiplying the value by 2. If the value passed to the myFunction() function is not a number, then the function will return null.
The Maybe monad can be used to deal with the possibility of values that are not of the expected type.
const myFunction = x =>
Maybe.of(x)
.map(x => {
if (typeof x !== 'number') {
throw new Error('x must be a number!');
}
return x * 2;
})
.getOrElse(null);
myFunction(10); // 20
myFunction('10'); // null
In the example above, the myFunction() function takes a value as an argument and returns the result of multiplying the value by 2. If the value passed to the myFunction() function is not a number, then the function will return null.
The Maybe monad