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find_value.js

// find_value.js

const arr = ['a', 'b', 'c', 'd'];
const stopAt = 'c';

console.log(
  arr.findIndex((...args) => {
    console.log('args', args);
    if (args[0] === stopAt) return true;
    return false;
  })
);

const findValue = (arr, fn) => {
  const idx = arr.findIndex(fn);
  if (idx === -1) return;
  return arr[idx];
};

console.log('-----');

Array.prototype.findValue = function(fn) {
  return findValue(this, fn);
};

console.log(
  arr.findValue((...args) => {
    console.log('args', args);
    if (args[0] === stopAt) return true;
    return false;
  })
);