fCC: Intermediate Algorithm Scripting: Everything Be True

truthy_falsy.js

//Check if the predicate (second argument) is truthy on all elements of a collection (first argument).

function truthCheck(collection, pre) {
  // .every returns one value if EVERY object statifies the test.
  // !! (double bang) typecasts the property value to a boolean value.
  // It will return true if the property value is truthy & false if the property doesn't exist/has a falsy value.
  return collection.every(obj => !!obj[pre]);  
}

truthCheck([{"user": "Tinky-Winky", "sex": "male"}, {"user": "Dipsy", "sex": "male"}, {"user": "Laa-Laa", "sex": "female"}, {"user": "Po", "sex": "female"}], "sex");
truthCheck([{"user": "Tinky-Winky", "sex": "male"}, {"user": "Dipsy"}, {"user": "Laa-Laa", "sex": "female"}, {"user": "Po", "sex": "female"}], "sex")

I didn't have to do too much research on this one because I've encountered truthy and falsy values before.

I started out with .forEach() and nested if statements using .hasOwnProperty() and then bracket notation (obj[pre])to access the value of the relevant property, but that obviously returned many boolean values and what I wanted was one to indicate whether ALL elements satisfied the condition.

Enter .every() and the little bit of research I did do to find out whether there was a better way to evaluate the truthiness of a property value than obj[pre] === true. It turns out there are multiple ways and they all have their pros and cons. It looked like the double bang (gotta love that name) property lookup is what I was looking for.

(I bookmarked the article that introduced me to my new fave because I have a feeling I'll be needing it again.)