一、什么是回调地狱:
人们普遍以javaScript
的执行顺序来编写代码,在执行异步代码时,无论以什么顺序简单的执行代码,通常情况会变成许多层级的回调函数堆积
<!DOCTYPE html> <html lang="en"> <head> <meta charset="UTF-8"> <meta name="viewport" content="width=device-width, initial-scale=1.0"> <title>Document</title> <!--通过ajax请求Id,再根据id请求用户名,再根据用户名去获取用户的邮箱--> <script src="./jquery-3.3.1.min.js"></script> </head> <body> <script> //发送ajax请求 $.ajax({ type:'GET', url:'./data1.json', success:(res)=>{ const {id} = res; console.log(id); //1 $.ajax({ type:'GET', url:'./data2.json', data:{id}, //相当于 id:id success:res1=>{ const {name} = res1 console.log(name);//张三 //再根据username获取email $.ajax({ type:'GET', url:'./data3.json', data:{name}, success:res3=>{ const { email } = res3; console.log(email);//486566947@qq.com } }); } }); } }); </script> </body> </html>