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'

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