composing function adding new parameter

user_12285495 0
Viewed 69

I'm currently learning JavaScript and got stuck by adding a parameter to my function that should add two numbers. I'm not new to programming. Did a lot in Java and C#, but Javascript drives me crazy with scope and compose and currying.... So here is my problem: 

const compose = (f, g) => (a) => f(g(a));
const add1 = (num) => num + 1;
const add5 = (num) => num + 5;
compose(add1, add5)(10)          // 16

The code above works! But i want that the +1 and +5 number to be variable so that i can have like this: 

// Something linke this 
const compose = (f, g) => (a,b) => f(g(a,b));
const add1 = (num, num2) => num + num2;
const add5 = (num, num2) => num + num2;
compose(add1, add5)(10, 4)   // Those numbers should be the Parameter input for add1 and add5 (num, num2)
parameters function functional-programming javascript
2 Answers

Maybe like this:

    const addN = (n) => num => num + n
    const compose = (f,g) => a => f(g(a));
    const result = compose(addN(10),addN(4))(1);
    console.log(result);

addN creates adder functions, in this case an add10 and an add4. Instead of returning a value as your original add1 and add5 did, addN is returning a function like add1 and add5 except it isn't hardcoded to be +1 or +5; it is + whatever you passed in when you called addN.

console.log(addN(6)(10)); //16

addN(6) creates an "add6" function, and then we call that "add6" function with 10 to get the output of 16

user_27632500

You can also use curried function like this to achieve the same in a better / simpler way without composing it.

// add = a => b => Number
const add = a => b => a + b;

const result = add(2)(3); // => 5

First, the function takes a, and then returns a new function, which then takes b returns the sum of a and b. Each argument is taken one at a time. If the function had more parameters, it could simply continue to return new functions until all of the arguments are supplied and the application can be completed.

user_97390440
Related