When the following statement is called when the page has not been loaded, the "add" object cannot be obtained, and the prompt is empty or not an object
document.getElementById("add").onclick = function(){
alert("hello");
}
Objects that are available when used
window. onload = function(){
document.getElementById("add").onclick = function(){
alert("hello");
}
}
![[Web front-end] Node.js quick start](https://img.php.cn/upload/course/000/000/067/662b5d34ba7c0227.png)
