Question

我有下面的JavaScript代码段。简而言之，我想要实现的目标是什么;检查传递给函数的参数是否是某些预定类的实例的方法。我知道我可以使用

if(obj instanceof className){ /* do stuff * / } else{ /* other things */ }

语句但是代码很庞大，特别是如果我有一堆类要测试的话。简而言之，我怎样才能实现下面代码的尝试？谢谢大家。

＆＃13;

class A {
    constructor(name) {
        this._name = name;
    }
}
class B {
    constructor(name) {
        this._name = name;
    }
}
class C {
    constructor(name) {
        this._name = name;
    }
}
let allTemplates = ['A', 'B', 'C', 'Object']; //available classes

let a = new A('A class');
let b = new B('B class');
let c = new C('C class');

function seekTemplateOf(obj) {
    /**find if @arg obj is an instance of any
     ** of the classes above or just an object
     **@return string "class that obj is instance of"
     **/
    return allTemplates.find(function(template) {
        return obj instanceof window[template];
        /*Thought that ^^ could do the trick?*/
    });
}
console.log(seekTemplateOf(a));
/*"^^ Uncaught TypeError: Right-hand side of 'instanceof' is not an object"*/

＆＃13;

Answer 1

将字符串更改为引用：

var dates = ["02/07/2018-02/07/2018", "02/05/2018-02/07/2018", "02/06/2018-02/06/2018", "02/08/2018-02/08/2018"];
var overlaps = checkOverlaps(dates);

console.log("overlaps", overlaps);

var dates1 = ["02/07/2018-02/07/2018", "02/08/2018-02/10/2018", "02/19/2018-02/20/2018", "02/21/2018-02/21/2018"];
var nonoverlaps = checkOverlaps(dates1);

console.log("nonoverlaps", nonoverlaps);

var dates2 = ["02/07/2018-02/07/2018", "02/07/2018-02/10/2018"]; /* 2nd range starts on the end of the first range */
var overlaps2 = checkOverlaps(dates2);

console.log("overlaps", overlaps2);

function checkOverlaps(dates) {
  var o = false;

  for (var key1 in dates) {
    var cDateArr = dates[key1].split("-");
    var d1 = new Date(cDateArr[0]);
    var d2 = new Date(cDateArr[1]);

    for (var key2 in dates) {

      //make sure not comparing to own self
      if (key1 != key2) {
        var cDateArrB = dates[key2].split("-");
        var dB1 = new Date(cDateArrB[0]);
        var dB2 = new Date(cDateArrB[1]);

        if (
          (d1 < dB1 && d2 > dB1) ||
          (d1 < dB2 && d2 > dB2) ||
          cDateArr[0] == cDateArrB[0] ||
          cDateArr[0] == cDateArrB[1] ||
          cDateArr[1] == cDateArrB[0] ||
          cDateArr[1] == cDateArrB[1]
        ) {
          o = true;
        }
      }
    }
  }

  return o;
}

然后检查对象构造函数是否等于：

let allTemplates = [A, B, C, Object];

或者（如果某些原型黑客忘记设置const obj = new A; const objClass = allTemplates.find(c => obj.constructor === c);），您可能会获得明确的原型：

constructor

或者你可以简单地使用const obj = new A; const objClass = allTemplates.find(c => Object.getPrototypeOf(obj) === c.prototype);：

instanceof

Answer 2

您可以使用对象作为模板并再次检查给定对象。

class A { constructor(name) { this._name=name; } }
class B { constructor(name) { this._name=name; } }
class C { constructor(name) { this._name=name; } }

let allTemplates = { A, B, C, Object };

let a = new A('A class');
let b = new B('B class');
let c = new C('C class');

function seekTemplateOf(obj) {
    return Object.keys(allTemplates).find(template => obj instanceof allTemplates[template]);
}

console.log(seekTemplateOf(a));

Javascript-有没有办法通过对象名称将对象的instanceof测试为字符串

2 个答案: