Create a Function with Appended Partials in JavaScript

In JavaScript, partial functions let you predefine some arguments of another function and call it later with remaining ones, making code cleaner and reusable.

• Partial application predefines some arguments of a function for later use.
• Uses the spread (...) operator to handle fixed and dynamic arguments.
• Helps create reusable and simplified versions of complex functions.

[Approach 1]: Using the Spread Operator to Append Partials

We want to implement a function that invokes another function and provides the arguments it received.

• We can get the result by using (...) the spread operator.
• Create a main function (math) that passes received arguments to another function.
• The first argument is the target function name; the rest (...params) are its parameters.
• Use the spread operator (...params) to call the target function with those arguments.
• Define helper functions like sum, sub, mul, and pow to perform operations using the passed arguments.

    // Function "math" responsible for
    // passing the arguments
    const math = (functionName, 
        ...params) => functionName(...params);
    
    //function to add all passed arguments
    const sum = (...args) => {
        var result = 0;
        for (const val of args) {
            result += val;
        }
        console.log(result);
    }
    
    // Function to subtract all
    // passed arguments
    const sub = (...args) => {
        var result = 0;
        for (const val of args) {
            result -= val;
        }
        console.log(result);
    }
    
    // Function to multiply all
    // passed arguments
    const mul = (...args) => {
        var result = 0;
        for (const val of args) {
            result *= val;
        }
        console.log(result);
    }
    
    // Call to the functions via "math"
    math(sum, 2, 3, 4, 5, 6);
    math(sub, 5, 4, 1);
    math(mul, 2, 3, 5, 6);

Output: The math function has successfully called the other functions and appended the required arguments.

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[Approach 2]: Using Rest Parameters for Partial Application

• following example demonstrates a function that uses the first two arguments.
• It has used the first two arguments and our "args" is referring to the rest of the arguments leaving the first two arguments.

    const fun = (arg1, arg2, ...args) => {
        console.log(args);
    }
    
    fun(1, 2, 3, 4, 5, 6);

Output:

[ 3, 4, 5, 6 ]