12. What is a unary function?

A unary function is a function that takes exactly one argument.

Example of a Unary Function:

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function square(x) {
  return x * x;
}

console.log(square(5)); // Output: 25

Here, square is a unary function because it accepts only one parameter (x).

Unary Functions in JavaScript:

Unary functions are common in functional programming, especially with methods like map and filter.

Example 1: Using a Unary Function in map

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const numbers = [1, 2, 3];
const doubled = numbers.map(x => x * 2); // Unary function (x => x * 2)
console.log(doubled); // Output: [2, 4, 6]

Special Case: unary() Function from Lodash

In JavaScript, functions may receive more arguments than defined. To enforce unary behavior, you can use Function.prototype.length or utilities like Lodash’s unary().

Example 2: Forcing Unary Behavior

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const unary = fn => arg => fn(arg);

const parse = unary(parseInt);
console.log(["1", "2", "3"].map(parse)); // Output: [1, 2, 3]

Without unary(), parseInt would receive unexpected arguments in map, leading to incorrect results.

Summary:

• A unary function takes exactly one argument.
• Commonly used in functional programming.
• Helps prevent unintended behavior when working with functions like map().

Would you like more examples or explanations?