javascript watch method event object

JavaScript is a scripting programming language that is often used to add dynamic functionality to Web pages. In JavaScript, there are many built-in events that can be triggered. When writing JavaScript code, we can use the watch method to monitor these event objects to make the web page dynamic.

The watch method is a built-in method in JavaScript that is used to monitor property changes of an object and perform some operations when the property value is modified. This method usually requires passing in two parameters: the name of the property to be monitored and the name of the method or callback function to be executed. When the monitored property value changes, JavaScript will automatically execute this method.

In practical applications, the watch method is often used to monitor a series of user interactive events such as mouse events, keyboard events, and form events. Take monitoring mouse movement events as an example. In the HTML document, we can add the following code:

<div id="box" onmouseover="showCoords(event)">
  <p>当前鼠标坐标：</p>
  <p id="demo"></p>
</div>

In this code, we use the onmouseover attribute of HTML to bind the showCoords function to the mouse movement event. . The showCoords function is a JavaScript function that displays the coordinates of the mouse movement in the demo element of the web page:

function showCoords(event) {
  var x = event.clientX;
  var y = event.clientY;
  var coords = "X坐标: " + x + ", Y坐标: " + y;
  document.getElementById("demo").innerHTML = coords;
}

In this function, we receive an event parameter, which represents the event object. The event object contains a series of information such as the element that triggered the event, mouse position, keyboard keys, etc. Here, we use event.clientX and event.clientY to obtain the mouse position and display this information on the web page.

Back to the watch method, we can use the watch method to monitor this event object. When the event object changes, JavaScript will automatically execute the callback function passed in. For example:

document.querySelector('#box').addEventListener('mousemove', function (event) {
  console.log(event.clientX, event.clientY);
})

In this code, we use the DOM's addEventListener method to bind a callback function to the mousemove event. This callback function outputs the mouse position information to the console. When the user moves the mouse, JavaScript will automatically trigger the mousemove event to execute this callback function.

In addition to mouse events, JavaScript also supports monitoring a series of events such as keyboard events and form events. We can use the watch method to monitor these event objects to make the web page dynamic.

In short, JavaScript's watch method can monitor event objects. When writing JavaScript dynamic effects, we can use this method to monitor user interactive events such as mouse, keyboard, and form. By monitoring these event objects, we can make web pages more interactive and improve user experience.

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