freeCodeCamp Intermediate Algorithm Scripting: Everything Be True

truthCheck.js

// Check if the predicate (second argument) is truthy on all 
// elements of a collection (first argument).
// In other words, you are given an array collection of objects. 
// The predicate pre will be an object property and you need to 
// return true if its value is truthy. Otherwise, return false.

// In JavaScript, truthy values are values that translate to true 
// when evaluated in a Boolean context.

// Remember, you can access object properties through either dot 
// notation or [] notation.


function truthCheck(collection, pre) {
  // Is everyone being true?
  return collection.reduce((status, person) => 
    (status && person.hasOwnProperty(pre) && !!person[pre]),
    true);
}


truthCheck([{"user": "Tinky-Winky", "sex": "male"}, 
{"user": "Dipsy", "sex": "male"}, 
{"user": "Laa-Laa", "sex": "female"}, 
{"user": "Po", "sex": "female"}], "sex"); // true.
truthCheck([{"user": "Tinky-Winky", "sex": "male"}, 
{"user": "Dipsy"}, {"user": "Laa-Laa", "sex": "female"}, 
{"user": "Po", "sex": "female"}], "sex"); // false.
truthCheck([{"user": "Tinky-Winky", "sex": "male", "age": 0}, 
{"user": "Dipsy", "sex": "male", "age": 3}, 
{"user": "Laa-Laa", "sex": "female", "age": 5}, 
{"user": "Po", "sex": "female", "age": 4}], "age"); // false.
truthCheck([{"name": "Pete", "onBoat": true}, 
{"name": "Repeat", "onBoat": true}, 
{"name": "FastFoward", "onBoat": null}], "onBoat"); // false
truthCheck([{"name": "Pete", "onBoat": true}, 
{"name": "Repeat", "onBoat": true, "alias": "Repete"}, 
{"name": "FastFoward", "onBoat": true}], "onBoat"); // true
truthCheck([{"single": "yes"}], "single"); // true
truthCheck([{"single": ""}, {"single": "double"}], "single"); // false
truthCheck([{"single": "double"}, {"single": undefined}], "single"); // false
truthCheck([{"single": "double"}, {"single": NaN}], "single"); // false