JS predicates, array filter and the use of predicates in array filter

Array filter

var ages = [32, 33, 16, 40];

function checkAdult(age) {
  return age >= 18;
}

function myFunction() {
  document.getElementById("demo").innerHTML = ages.filter(checkAdult);

}

https://www.w3schools.com/jsref/jsref_filter.asp


Predicates

function or(p1, p2) {
    return function(x) {
        return p1(x) || p2(x);
    }
}
The function or consumes two predicates p1 and p2, and returns a new predicate. That returned predicate tests a value x and returns true if either p1(x) is true or p2(x) is true. Let's test it out with the two predicates negative and positive:

function negative(x) {
    return x < 0;
}
function positive(x) {
    return x > 0;
}
var nonzero = or(negative, positive);
alert(nonzero(-5));
alert(nonzero(0));

alert(nonzero(5));

https://codepen.io/Universalist/post/predicates-in-javascript

Predicates used to find diff in array objects:

a = [{ value:"4a55eff3-1e0d-4a81-9105-3ddd7521d642", display:"Jamsheer"}, { value:"644838b3-604d-4899-8b78-09e4799f586f", display:"Muhammed"}, { value:"b6ee537a-375c-45bd-b9d4-4dd84a75041d", display:"Ravi"}, { value:"e97339e1-939d-47ab-974c-1b68c9cfb536", display:"Ajmal"},  { value:"a63a6f77-c637-454e-abf2-dfb9b543af6c", display:"Ryan"}]
b = [{ value:"4a55eff3-1e0d-4a81-9105-3ddd7521d642", display:"Jamsheer", $$hashKey:"008"}, { value:"644838b3-604d-4899-8b78-09e4799f586f", display:"Muhammed", $$hashKey:"009"}, { value:"b6ee537a-375c-45bd-b9d4-4dd84a75041d", display:"Ravi", $$hashKey:"00A"}, { value:"e97339e1-939d-47ab-974c-1b68c9cfb536", display:"Ajmal", $$hashKey:"00B"}]

function comparer(otherArray){
  return function(current){
    return otherArray.filter(function(other){
      return other.value == current.value && other.display == current.display
    }).length == 0;
  }
}

var onlyInA = a.filter(comparer(b));
var onlyInB = b.filter(comparer(a));

result = onlyInA.concat(onlyInB);

console.log(result);

https://stackoverflow.com/questions/21987909/how-to-get-the-difference-between-two-arrays-of-objects-in-javascript