Junior Developer Central JS Practice Exercise - 20

 

Question: 

Write a Javascript function that returns true if the provided predicate function returns true for all elements in a collection, false otherwise. 

Answer: 

function checkFunction(arr, fn) {

  for (let i = 0; i < arr.length; i++) {

    if (!fn(arr[i])) {

      return false;

    }

  }

  return true;

}

> we declare a function 'checkFunction' 

> it has two parameters 'arr' & 'fn' 

> we want to return false if 'fn' (which is a function) returns false for even one element in 'arr' (which is an array)

> our function should return true if the function 'fn' returns true for all elements in array 'arr'

> so in order to check the result of the function 'fn' on each and every element of array 'arr' we use the for loop

>  we additionally use the if statement to check the boolean value on each iteration of the for loop

> we return false if the condition is met and the loop is terminated

> we keep the iterations running till all the elements of the array are checked and terminate the loop by returning 'true'