freeCodeCamp/guide/english/certifications/javascript-algorithms-and-data-structures/intermediate-algorithm-scripting/everything-be-true/index.md

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Everything Be True

Everything Be True

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Problem Explanation

The program needs to check if the second argument is a truthy element, and it must check this for each object in the first argument.

Relevant Links

• JavaScript Truthy
• JavaScript Arguments

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Hints

Hint 1

Remember to iterate through the first argument to check each object.

Hint 2

Only if all of them are truthy will we return true, so make sure all of them check.

Hint 3

You could use loops or callback functions, there are multiple ways to solve this problem.

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Solutions

Solution 1 (Click to Show/Hide)

Using for-in loop & hasOwnProperty

function truthCheck(collection, pre) {
  // Create a counter to check how many are true.
  var counter = 0;
  // Check for each object
  for (var c in collection) {
    // If it is has property and value is truthy
    if (collection[c].hasOwnProperty(pre) && Boolean(collection[c][pre])) {
      counter++;
    }
  }
  // Outside the loop, check to see if we got true for all of them and return true or false
  return counter == collection.length;
}

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

Code Explanation

• First I create a counter to check how many cases are actually true.
• Then check for each object if the value is truthy
• Outside the loop, I check to see if the counter variable has the same value as the length of collection, if true then return true, otherwise, return false

Relevant Links

• JS Loops
• Object.prototype.hasOwnProperty()

Solution 2 (Click to Show/Hide)

Using Array.every()

function truthCheck(collection, pre) {
  return collection.every(function(element) {
    return element.hasOwnProperty(pre) && Boolean(element[pre]);
  });
}

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

Code Explanation

• Uses the native "every" method to test whether all elements in the array pass the test.
• This link will help Array.prototype.every()

Relevant Links

• JS Array.prototype.every()
• MDN Array.prototype.every()

Solution 3 (Click to Show/Hide)

function truthCheck(collection, pre) {
  // Is everyone being true?
  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"
);

Code Explanation

• For every object in the collection array, check the truthiness of object's property passed in pre parameter
• Array#every method internally checks if the value returned from the callback is truthy.
• Return true if it passes for every object. Otherwise, return false.

Relevant Links

• Array#every