instanceof

一、JavaScript有几种类型的值？ Javascript有两种数据类型，分别是基本数据类型和引用数据类型。其中基本数据类型包括Undefined、Null、Boolean、Number、String、Symbol (ES6新增，表示独一无二的值)，而引用数据类型统称为Object对象，主要包括对象、数组和函数。接下来我们分别看下两者的特点。 二、基本数据类型 1.值是不可变的 var name = 'java'; name.toUpperCase(); // 输出 'JAVA' console.log(name); // 输出 'java' 由此可得，基本数据类型的值是不可改变的 2.存放在栈区 原始数据类型直接存储在栈(stack)中的简单数据段，占据空间小、大小固定，属于被频繁使用数据，所以放入栈中存储。 3.值的比较 var a = 1; var b = true; console.log(a == b); // true console.log(a === b); // false == : 只进行值的比较,会进行数据类型的转换。 === : 不仅进行值得比较，还要进行数据类型的比较。 三、引用数据类型 1.值是可变的 var a={age:20}； a.age=21； console.log(a.age)//21 上面代码说明引用类型可以拥有属性和方法

When redeclaring Integer 'a' in line 33, why does jshell show the reference variable as an instance of Integer (refer to lines 38 & 39)? After the redeclaration, line 34 shows that 'a' is set to null. When 'a' is declared in line 6 but not given a value, or reset to null in line 22, 'a' is not considered an instance of Integer. I would expect that when the reference variable is redeclared, since its value is null, that it would not be an instance of a type; however, that is not the case. 01: java-lava:~ cafedude$ jshell 02: | Welcome to JShell -- Version 11 03: | For an introduction type:

This question already has answers here : Closed 6 years ago . Why does `instanceof` error rather than return `false` when used for 2 incompatible classes? (4 answers) class A { public static void main(String...args) { Integer var = 10; if(var instanceof Character) // Line1 System.out.println("var is a Character"); } } I know Line 1 will not compile because the compiler has found that var is not a Character . What I fail to understand is why the compiler throws an error instead of returning false or true . If the compiler returns false or true (i.e treating the instanceof operation like a

Im overriding an equals() method and I need to know if the object is an instance of a Event's subclass (Event is the superclass). I want something like "obj subclassof Event". How can this be made? Thanks in advance! instanceof can handle that just fine. Adrian With the following code you can check if an object is a class that extends Event but isn't an Event class instance itself. if(myObject instanceof Event && myObject.getClass() != Event.class) { // then I'm an instance of a subclass of Event, but not Event itself } By default instanceof checks if an object is of the class specified or a

I need a method where i could pass on a parameter which i assume would be a Class (not sure though) and in that method, instanceof would be used to check if x is an instance of the passed Class. How should i do that? I tried a few things but none worked. How about this: public boolean checker(Object obj) { return obj instanceof SomeClass; } or if SomeClass is a parameter: public boolean checker(Object obj, Class someClass) { return someClass.isInstance(obj); } or if you want the instance to be someClass and NOT an instance of a subclass of someClass : public boolean checker(Object obj, Class

//js中最常用的继承方式--组合继承 function Super(name){ this.name = name; this.colors = ["red","blue","green"]; } Super.prototype.sayName = function(){ console.log(this.name); } function Sub(name){ //继承了属性 Super.call(this,name); } //继承了方法 Sub.prototype = new Super(); var sub1 = new Sub("Nick"); sub1.colors.push("black"); console.log(sub1.colors); //(4) ["red", "blue", "green", "black"] sub1.sayName(); //Nick var sub2 = new Sub("Lucy"); console.log(sub2.colors); //(3) ["red", "blue", "green"] sub2.sayName(); //Lucy 组合继承避免了原型链和借用构造函数的缺陷，融合了它们的优点，成为js中最常用的继承模式。 //返回的都是true console.log(sub1 instanceof Object);

My question is when how does the class info gets loaded during runtime? When someone calls instanceof is that considered RTTI or reflection? Or it depends on the actual situation? The term " RTTI " is a C++-specific term referring to the functionality of the core language that allows the program to determine the dynamic types of various objects at runtime. It usually refers to the dynamic_cast or typeid operators, along with the associated std::type_info object produced by typeid . The term reflection, on the other hand, is a generic term used across programming languages to refer to the

创建对象可能首先想到的就是字面的形式，比如这样的 <!--字面量--> var obj1 = { name: "张三", age: 18 } 但是这样创建对象，如果创建多个类似的对象就会有冗余代码，所以就有了各种模式来创建对象 第一种 工厂模式 function createPerson(name,age) { var o = new Object(); o.name = name; o.age = age; o.say = function(){ alert(this.name); } return o; } var person1 = createPerson("lisi",21); //instanceof无法判断它是谁的实例，只能判断他是对象，构造函数都可以判断出 var person2 = createPerson("wangwu",18); console.log(person1 instanceof Object); 这样虽然解决了代码的冗余，但是无法判断一个对象的类型 第二种 构造函数模式 /*构造函数模式*/ function Person(name,age) { this.name = name; this.age = age; this.say = function(){ alert(this.name); } } var person1 = new

本文首发于我的个人博客 ： http://cherryblog.site/ 前言 js 中的类型检测也是很重要的一部分，所以说这篇文章我们就来讲一下怎么对 JavaScript 中的基本数据类型进行检测。其实这也是在读 Zepto 源码中学习到的，所以阅读源码对我们的提升还是很有帮助的。本文基于参考了前辈们的文章之后个人理解此文写的有不当的地方，请各位大佬指正。 其实常规方法主要有四种 typeof instanceof Object.prototype.toString construcor 其实这四种方式归根结底就是两种思路： 根据数据类型判断（1，2） 根据构造函数判断（3，4） 前置基础 再看 Zepto 之前看了 慕课网一个老师的视频 ，一共一个小时左右，开了快进估计也就 45 分钟左右。只是讲了 Zepto 的架构和设计，没有详细的将每一个方法，初看之前可以看一下，对 Zepto 有一个大概的印象。 原型与原型链 其实这部分真的是老生常谈的问题，但是每一次听其他人都有新的收获。 真的是不想写这部分，但是自我感觉整体思路比较清晰 ，所以推荐大家阅读一下。 Zepto 整个的设计思想其实是基于 js 的原型链。关于原型链，这个老师讲的比较清晰，需要记住三句话： 每一个函数，都有一个 prototype 属性。 所有通过函数 new 出来的对象，这个对象都有一个 _