I have a filtering function and i pass a testing function into it:
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 id like to be able to write
console.log(filterArray(array,not(bigger)))
>>>[1,3,5]
You can create a function not that takes in a function and returns another function which returns the inverse of the 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)));You can do something like this:
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 idea is to have the isNot function return a function which simply negates the result of the passed as parameter function.
I would do something like the following.
var array = [1,3,5,7,9]
function bigger(n){return n > 5}
console.log(array.filter(element => !bigger(element)))
To account for variadic functions: Collecting arguments in an array "arguments" and passing them on to the function.
function not(myFunction){
if (typeof myFunction != "function"){return !myFunction }
return function (...arguments) {
return !myFunction.apply(null,arguments)
}
}
in short:
const not = f => (...a) => !f.apply(null,a)
Also to make it work for all values - check if a function has been passed. which also allows to use it like so not(bigger(1,2)):
function not(anything){
if (typeof anything != "function"){return !anything }
return function (...arguments) {
return !anything.apply(null,arguments)
}
}
var variable = true
console.log(not(bigger(6))) >>> true
console.log(not(variable))) >>> false
console.log(not(false))) >>> true
in short:
const not = f => typeof f != "function" ? !f : (...a) => !f.apply(null,a)