JS - this As A DOM Event Handler-优快云博客

博客介绍了编程中事件和事件处理程序的概念。事件是用户或其他来源触发的动作，如鼠标点击、按键等；事件处理程序是用于处理事件的例程，程序员可编写在事件发生时执行的代码，还提到了作为DOM事件处理程序的情况。

n programming, an event is an action that occurs as a result of the user or another source, such as a mouse being clicked, or a key being pressed.

An event handler is a routine that is used to deal with the event, allowing a programmer to write code that will be executed when the event occurs.

As a DOM event handler

When a function (bluify below) is used as an event handler, its this is set to the element the event fired from (some browsers do not follow this convention for listeners added dynamically with methods other than addEventListener()).

// When called as a listener, turns the related element blue
function bluify(e) {
  // Always true
  console.log(this === e.currentTarget); 
  // true when currentTarget and target are the same object
  console.log(this === e.target);
  this.style.backgroundColor = '#A5D9F3';
}

// Get a list of every element in the document
var elements = document.getElementsByTagName('*');

// Add bluify as a click listener so when the
// element is clicked on, it turns blue
for (var i = 0; i < elements.length; i++) {
  elements[i].addEventListener('click', bluify, false);
}