Within my filtering function, I am passing a testing function:
var array = [1,3,5,7,9]
function bigger(n){return n > 5}
function filterArray(data,testfn){
return data.filter(e=> testfn(e))}
console.log(filterArray(array,bigger))
>>>[7,9]
Now, I want to be able to write
console.log(filterArray(array,not(bigger)))
>>>[1,3,5]
One way to enhance your code is by creating a function called not. This function takes in another function as an argument and then returns a new function that provides the opposite result of calling the original function:
var array = [1, 3, 5, 7, 9];
function bigger(n) {
return n > 5
}
function filterArray(data, testfn) {
return data.filter(e => testfn(e))
}
function not(f) {
return function(n) {
return !f(n);
}
}
console.log(filterArray(array, bigger));
console.log(filterArray(array, not(bigger)));If you're looking to achieve a similar outcome, you could try implementing the following approach:
var array = [1, 3, 5, 7, 9]
const isBiggerThan = (n) => n > 5
const isNot = (fn) => (n) => !fn(n)
const filterArray = (data, testfn) => data.filter(e => testfn(e))
console.log(filterArray(array, isBiggerThan))
console.log(filterArray(array, isNot(isBiggerThan)))The concept behind this function setup involves using the isNot function to produce a new function that simply flips the result of the passed-in function.
In my approach, I typically use a similar strategy.
let numbers = [2,4,6,8,10];
const isSmaller = (num) => num <= 8;
console.log(numbers.filter(item => isSmaller(item)));
To handle variadic functions: Gathering arguments in an array named "arguments" and passing them to the function.
function not(myFunction){
if (typeof myFunction != "function"){return !myFunction }
return function (...args) {
return !myFunction.apply(null,args)
}
}
In summary:
const not = f => (...a) => !f.apply(null,a)
Additionally, to ensure it works for all values - checking if a function is being passed. This allows using it like this not(bigger(1,2)):
function not(anything){
if (typeof anything != "function"){return !anything }
return function (...args) {
return !anything.apply(null,args)
}
}
var variable = true
console.log(not(bigger(6))) >>> true
console.log(not(variable))) >>> false
console.log(not(false))) >>> true
In summary:
const not = f => typeof f != "function" ? !f : (...a) => !f.apply(null,a)
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