function _findIndex(arr, onFind) {
  let foundIndex = -1;

  util.forEach(arr, (item, index) => {
    let nextFind = true;
    if (onFind(item, index)) {
      foundIndex = index;
      nextFind = false;
    }

    return nextFind;
  });

  return foundIndex;
}
function _findIndex(arr, onFind) {
  let foundIndex = -1;

  util.forEach(arr, (item, index) => {
    let nextFind = true;
    if (onFind(item, index)) {
      foundIndex = index;
      nextFind = false;
    }

    return nextFind;
  });

  return foundIndex;
}
function _findIndex ( arr , onFind ) { let foundIndex = - 1 ; util . forEach ( arr , ( item , index ) => { let nextFind = true ; if ( onFind ( item , index ) ) { foundIndex = index ; nextFind = false ; } return nextFind ; } ) ; return foundIndex ; }
Find index by onFind function.
@param {Array} arr - target array
@param {function} onFind - find function
@returns {number}
@private
Find index by onFind function .
Find index of an item in an array