document.ready 是指文檔加載好, dom 加載好,僅包含在它以前的 script 、css 標籤 , 但不包含 img 標籤是否加載完成, 由於頁面是按順序執行的。javascript
onload 是指頁面徹底加載好,包括全部節點,甚至 img 標籤css
固然咱們編碼通常都是把基礎庫放在head 頭部,保證最早加載,業務代碼放在最後,避免出現庫未加載完成的狀況。html
固然如今前端工程通常使用 webpack 等打包技術,在編譯打包過程當中就徹底實現了依賴項前置的功能。前端
<!DOCTYPE html> <html> <head> <title></title> </head> <body onload="onload()"> <img src="http://upload.chinaz.com/upimg/allimg/110630/0901070.jpg" /> <script type="text/javascript" src="http://libs.cdnjs.net/jquery/3.2.1/jquery.min.js"></script> <script type="text/javascript"> $(document).ready(function() { console.log('document ready'); }); </script> <script type="text/javascript"> console.log('haha'); </script> </body> <script type="text/javascript"> function onload() { console.log('onload'); } </script> </html> // 打印 //haha //document ready //onload
<!DOCTYPE html> <html> <head> <title></title> </head> <body onload="onload()"> <img src="http://upload.chinaz.com/upimg/allimg/110630/0901070.jpg" /> <script type="text/javascript"> $(document).ready(function() { console.log('document ready'); }); </script> <script type="text/javascript"> console.log('haha'); </script> <script type="text/javascript" src="http://libs.cdnjs.net/jquery/3.2.1/jquery.min.js"></script> </body> <script type="text/javascript"> function onload() { console.log('onload'); } </script> </html> //打印 //$ undefined //haha //onload
<!DOCTYPE html> <html> <head> <title></title> </head> <body onload="onload()"> <img src="http://upload.chinaz.com/upimg/allimg/110630/0901070.jpg" /> <script type="text/javascript"> console.log('haha'); </script> <script type="text/javascript"> $(document).ready(function() { console.log('document ready'); }); </script> <script type="text/javascript" src="http://libs.cdnjs.net/jquery/3.2.1/jquery.min.js"></script> </body> <script type="text/javascript"> function onload() { console.log('onload'); } </script> </html> //打印 //haha //$ undefined //onload