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We have a built-in method arr.filter(f) for arrays. It filters all elements through the function f. If it returns true, then that element is returned in the resulting array.

Make a set of ready to use filters:

inBetween(a, b) between a and b or equal to them (inclusively).
inArray([...]) in the given array.

The usage must be like this:

arr.filter(inBetween(3,6)) selects only values between 3 and 6.
arr.filter(inArray([1,2,3])) selects only elements matching with one of the members of [1,2,3].

For instance:

          /* .. your code for inBetween and inArray */
let arr = [1, 2, 3, 4, 5, 6, 7];

alert( arr.filter(inBetween(3, 6)) ); // 3,4,5,6

alert( arr.filter(inArray([1, 2, 10])) ); // 1,2

Open a sandbox with tests.

solution

Filter inBetween

function inBetween(a, b) {
  return function(x) {
    return x >= a && x <= b;
  };
}

let arr = [1, 2, 3, 4, 5, 6, 7];
alert( arr.filter(inBetween(3, 6)) ); // 3,4,5,6

Filter inArray

function inArray(arr) {
  return function(x) {
    return arr.includes(x);
  };
}

let arr = [1, 2, 3, 4, 5, 6, 7];
alert( arr.filter(inArray([1, 2, 10])) ); // 1,2

Open the solution with tests in a sandbox.

Filter through function

Filter inBetween

Filter inArray