javascript - Function only returns true for first element in array

Question

I am trying to write a function that will return true if either 'purple' or 'magenta' elements are present in an array. However my code will only return true when either purple or magenta are the first item in the array:

function containsPurple(arr) {
  for (let i = 0; i < arr.length; i++) {
    if (arr[i] === 'purple' || arr[i] === 'magenta') {
      return true;
    }
    return false;
  }
}

So for example, containsPurple(['black', 'magenta', 'yellow']) returns false, however containsPurple(['magenta', 'black', 'yellow']) returns true. Where am I going wrong?

question from:https://stackoverflow.com/questions/65902660/function-only-returns-true-for-first-element-in-array

Answer 1

Consider your condition:

if (arr[i] === 'purple' || arr[i] === 'magenta') {
  return true;
}
return false;

Let's assume that arr[i] === 'orange'. Does it match your if-condition? No. So it continues to the next line, which is return false. Once a function encounters a return statement, the function is completed and the return value is returned. Never will your loop go to the next iteration, because in the first iteration it will always encounter a return statement (it be either return true or return false).

To fix this you can move the return false outside of your loop. This way it will keep looping until any iteration matches the if condition. If not, it will exit the loop and continue to the return false and finish the function with the return value false.

function containsPurple(arr) {
  for (let i = 0; i < arr.length; i++) {
    if (arr[i] === 'purple' || arr[i] === 'magenta') {
      return true;
    }
  }
  return false;
}

console.log('black, yellow', containsPurple(['black', 'yellow']));
console.log('black, magenta, yellow', containsPurple(['black', 'magenta', 'yellow']));
console.log('magenta, black, yellow', containsPurple(['magenta', 'black', 'yellow']));