Currying is a functional programming technique used in JavaScript where a function that takes multiple arguments is transformed into a sequence of functions, each accepting a single argument. This allows you to partially apply arguments, providing a more flexible way of working with functions.
Currying is the process of transforming a function that takes multiple arguments into a series of functions that each take a single argument. The first function will take the first argument, return a new function that takes the second argument, and so on, until all arguments have been provided.
A basic example of currying can be illustrated as follows:
function add(a) { return function(b) { return a + b; }; } const addFive = add(5); // The first function is called with 5 console.log(addFive(3)); // Output: 8 (5 + 3)
In the example above:
Currying is most useful when you have a function that takes multiple arguments and you want to break it down into smaller, reusable pieces. Here’s an example of currying with multiple arguments:
function multiply(a) { return function(b) { return function(c) { return a * b * c; }; }; } const multiplyBy2 = multiply(2); // First argument is fixed as 2 const multiplyBy2And3 = multiplyBy2(3); // Second argument is fixed as 3 console.log(multiplyBy2And3(4)); // Output: 24 (2 * 3 * 4)
In this case:
You can implement currying manually by creating a function that takes a number of arguments and returns a function that accumulates those arguments.
function curry(fn) { return function curried(...args) { if (args.length >= fn.length) { return fn(...args); } else { return function(...newArgs) { return curried(...args, ...newArgs); }; } }; } // Example function function sum(a, b, c) { return a + b + c; } const curriedSum = curry(sum); console.log(curriedSum(1)(2)(3)); // Output: 6
In the example above:
Currying allows you to create more reusable and composable functions. It can simplify the code in some scenarios and make it easier to work with functions that share common arguments.
Partial Function Application: Currying enables partial application of functions, meaning you can create specialized functions by fixing some arguments and leaving others to be provided later.
Function Composition: You can combine curried functions to build more complex operations without having to repeat code.
Improved Readability: Currying makes it clear which arguments a function needs, and allows for cleaner, more concise code.
function add(a) { return function(b) { return a + b; }; } const addFive = add(5); // The first function is called with 5 console.log(addFive(3)); // Output: 8 (5 + 3)
Here, multiplyBy10 is a specialized function that has the first argument fixed to 10. This can be reused in multiple places.
Suppose you are making a series of API requests with common parameters. Currying can be used to simplify this process.
function multiply(a) { return function(b) { return function(c) { return a * b * c; }; }; } const multiplyBy2 = multiply(2); // First argument is fixed as 2 const multiplyBy2And3 = multiplyBy2(3); // Second argument is fixed as 3 console.log(multiplyBy2And3(4)); // Output: 24 (2 * 3 * 4)
While currying transforms a function into a series of unary functions, partial application is the process of fixing some arguments of a function and returning a new function that accepts the remaining arguments. Currying is one way to achieve partial application.
function curry(fn) { return function curried(...args) { if (args.length >= fn.length) { return fn(...args); } else { return function(...newArgs) { return curried(...args, ...newArgs); }; } }; } // Example function function sum(a, b, c) { return a + b + c; } const curriedSum = curry(sum); console.log(curriedSum(1)(2)(3)); // Output: 6
Here, we partially applied "Hello" to the greet function using bind().
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