# 章序号/节序号/节/笔记序号
codecademy, Condition
# 概念阐释
# 举例子
# 类比、比较与对比
# 问题
[RaceDay](https://www.codecademy.com/courses/introduction-to-javascript/projects/race-day)
As a timeline, registration would look like this:
Here’s how our registration works. There are **adult runners (over 18 years of age)** and **youth runners (under 18 years of age)**. They can register **early or late**. Runners are assigned a race number and start time based on their age and registration.
Race number:
- **Early adults** receive a race number **at or above 1000**.
- **All others** receive a number below 1000.
Start time:
- **Adult** registrants run at 9:30 am **or** 11:00 am.
- **Early adults** run at 9:30 am.
- **Late adults** run at 11:00 am.
- **Youth** registrants run at 12:30 pm (regardless of registration).
But we didn’t plan for runners that are exactly 18! We’ll handle that by the end of the project.
# 问题答案
[codecademy](https://www.codecademy.com/courses/introduction-to-javascript/projects/race-day)
```js
let raceNumber = Math.floor(Math.random()*1001);
let registerEarly=true;
let runnerAge= 18;
//满足准时报道的成年人，发放1000以上的号码,改变race number的变量
if(registerEarly===true && runnerAge>18){
raceNumber+=1000;
};
//准时报道的成年人，在9:30开始比赛
if(registerEarly===true && runnerAge>18 ){
console.log('race will begin at 9:30, and your race number is ' + raceNumber);//这里的raceNumber符合上面的if条件
}else if(registerEarly===false && runnerAge>18){
console.log('race will begin at 11:30, and your race number is '+ raceNumber);//因为在前面已经创建了条件，必须是18岁以上早到的成年人才会满足random number+1000,否则为random number，1000以下
}else if(runnerAge < 18){
console.log('youth will begin at 12:00, and your race number is '+ raceNumber);
}else{
console.log('Please approach the registration desk,thanks!')
}//只剩下=18这个条件了
```
# 备注（经验集/错误集）
- 重要的是把可能的条件先列清楚