[英]How can i find specific new object of Class that has a constructor argument equal to input
我有一个名为Country的类,带有4个构造函数参数。
然后,我使用指定的值从该类创建一些新的国家/地区。
我的问题是,如何创建一个方法,可以找到并返回一个this.value等于方法输入的对象?
class Country {
constructor(name, area, population, topdomain) {
this.name = name;
this.area = area;
this.population = population;
this.topdomain = topdomain;
}
static findCountry = domain => {
/*Here is where the magic should happen.
If domain is in any of the countries below, then it should return the country name.
*/
}
}
norway = new Country("Norway", 323802, 5320045, ".no");
sweden = new Country("Sweden", 450295, 9960487, ".se");
russia = new Country("Russia", 17098242, 142257519, ".ru");
china = new Country("China", 9596960, 1379302771, ".cn");
这个函数应该返回“Norway”:
Country.findCountry(".no");
要使其工作,该类必须保留所有已创建实例的列表。 由于JS没有弱引用,这意味着没有任何实例可以被垃圾收集(所以要小心):
static instances = [];
constructor(/*...*/) {
/*...*/
Country.instances.push(this);
}
static findCountry = domain => {
return this.instances.find(country => country.domain === domain);
}
不要来这里要求别人写你的代码;)
class Country {
constructor(name, area, population, topdomain) {
this.name = name;
this.area = area;
this.population = population;
this.topdomain = topdomain;
Country._ALL.push(this);
}
static findBy(key, value) {
let output = [];
for ( let i in Country._ALL) {
let c = Country._ALL[i];
if (c.hasOwnProperty(key) && c[key] === value)
output.push(c);
}
return output;
}
}
Country._ALL = [];
警告! ES6类不支持静态变量,如static variable = [];
如果你想在ES6中使用静态类变量,你必须使用ClassName.variable = [];
之后类的声明。
你的类不知道你在某处实例化的4个对象。 您需要将它们放在一个集合(例如数组)中,然后在搜索方法中显式引用该集合:
class Country {
constructor(name, area, population, topdomain) {
this.name = name;
this.area = area;
this.population = population;
this.topdomain = topdomain;
}
static findCountry(domain) {
return (knownCountries.find(country => country.topdomain == domain) || {}).name;
// ^^^^^^^^^^^^^^
}
}
const norway = new Country("Norway", 323802, 5320045, ".no");
const sweden = new Country("Sweden", 450295, 9960487, ".se");
const russia = new Country("Russia", 17098242, 142257519, ".ru");
const china = new Country("China", 9596960, 1379302771, ".cn");
const knownCountries = [norway, sweden, russia, china];
// ^^^^^^^^^^^^^^
声明:本站的技术帖子网页,遵循CC BY-SA 4.0协议,如果您需要转载,请注明本站网址或者原文地址。任何问题请咨询:yoyou2525@163.com.