Question

嗨，我是React的新手。我正在开发任务，我需要声明一个具有空值的数组：

this.state = {
  position: [null,null,null,null,null,null,null,null]
};

此后，我为该数组分配了一些值，但是我的应用程序确实要求每个池只能更改一次。问候

Answer 1

如果将任务更改为 admin_routes: host: "admin.{domain}" resource: "@AppBundle/Controller/Admin" type: annotation requirements: domain: domain.local|domain2.local defaults: { domain: domain.local } user_routes: host: "user.{domain}" resource: "@AppBundle/Controller/User" type: annotation requirements: domain: domain3.local|domain4.local defaults: { domain: domain3.local }，只能将其从position更改为另一个值，而不能再次更改为null ，则此操作很容易

null

Answer 2

您可以为此使用Proxy

let arr = Array(5).fill(null);
const validator = {
  set:function(obj,prop,value){
    if(obj[prop] !== null) throw "You can't change it again"
    else obj[prop] = value;
  }
}
var p = new Proxy(arr, validator);
p[1] = 2; //the element is successfully changed
console.log(JSON.stringify(p))

p[1] = 3; // changing again throw error.

如何使数组的每个池只能分配一次

2 个答案: