1. <!DOCTYPE html>
    2. <html lang="en">
    3. <head>
    4.     <meta charset="UTF-8">
    5.     <meta name="viewport" content="width=device-width, initial-scale=1.0">
    6.     <title>Document</title>
    7.     <script src="js/index.js"></script>
    8. </head>
    9. <body>
    10.     <p id="p">hello world</p>
    11. </body>
    12. </html>

    页面加载完毕之后才会触发

    /* 页面加载完毕之后才会触发 */
window.onload = function () {
    var p = document.getElementById("p");
    p.onclick = function () {
        console.log("hello world")
    }
}