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Function Parameters Question

I am working through the build a to do app with JS project and noticed something interesting from the instructor.

He seems to be using the parameter names as an object. For example below taskListItem and checkBoxEventHandler are only parameter names, they do not exist anywhere else in the program as variables yet he is able to access object properties and methods with them such as querySelector.

var bindTaskEvents = function(taskListItem, checkBoxEventHandler) {
  console.log('bind list item events');

  var checkBox = taskListItem.querySelector('input[type=checkbox]');
  var editButton = taskListItem.querySelector('button.edit');
  var deleteButton = taskListItem.querySelector('button.delete');

  editButton.onclick = editTask;
  deleteButton.onclick = deleteTask;
  checkBox.onchange = checkBoxEventHandler; 

for (var i = 0; i < incompleteTasksHolder.children.length; i++) {
  bindTaskEvents(incompleteTasksHolder.children[i], taskCompleted);

for (var i = 0; i < completedTasksHolder.children.length; i++) {
  bindTaskEvents(completedTasksHolder.children[i], taskIncomplete);

I was unaware that you could perform methods() or check properties using a parameter name. To clarify, is that whats going on here?

1 Answer

Looks like you can manipulate parameters in this manner. News to me, for anyone reading eager for an answer as well, look at this example:

var dogVar = 'dog';
var catVar = 'cat';

function stringCheck (string, string2) {
  console.log(string.length + string2.length);

stringCheck(dogVar, catVar);