instanceof

构造函数方法创建对象

由 ￡可爱￡侵袭症＋ 提交于 2019-12-11 01:59:21
㈠构造函数 创建一个构造函数，专门用来创建Person对象的 构造函数就是一个普通的函数，创建方式和普通函数没有区别, 不同的是构造函数习惯上首字母大写 构造函数和普通函数的 区别就是调用方式的不同 普通函数 是 直接调用 ，而 构造函数 需要 使用new关键字来调用 示例：创建一个构造函数 function Person(){ alert(this); } var per = new Person(); console.log(per); 浏览器中显示为： ㈡构造函数的执行流程 1.立刻创建一个新的对象 2.将新建的对象设置为函数中this,在构造函数中可以使用this来引用新建的对象 3.逐行执行函数中的代码 4.将新建的对象作为返回值返回 具体示例如下： function Person(name , age , gender){ this.name = name; this.age = age; this.gender = gender; this.sayName = function(){ alert(this.name); }； } var per = new Person("孙悟空",18,"男"); var per2 = new Person("玉兔精",16,"女"); var per3 = new Person("奔波霸",38,"男"); console.log

Angular——路由跳转/传参/监听路由

由 ∥☆過路亽．° 提交于 2019-12-11 00:48:23
constructor( private router: Router, private route: ActivatedRoute, ） { } if (event instanceof NavigationEnd) { if (this.route.snapshot.queryParams.id) { this.queryList.FileId = this.route.snapshot.queryParams.id; this.queryList.Offset = 0; } } this.router.navigate(['home/document/pulicDoc'], {queryParams: {id: res}}); this.isDocument = this.router.events.subscribe((event: Event) => { if (event instanceof NavigationEnd) { this.fileActive = event.url.indexOf('pulicDoc') >= 0 || event.url.indexOf('proDoc') >= 0; } }); this.unSpace = this.userSpaceService.spaceChange$.subscribe(res => { this

How to go about understanding the type `new (…args: any[]) => any`

由 孤者浪人 提交于 2019-12-11 00:39:10
问题 I'm reading through the code of the class-validator library and it has the following isInstance method in it: /** * Checks if the value is an instance of the specified object. */ isInstance(object: any, targetTypeConstructor: new (...args: any[]) => any) { return targetTypeConstructor && typeof targetTypeConstructor === "function" && object instanceof targetTypeConstructor; } Any thoughts on how to go about understanding the type new (...args: any[]) => any ? This is the first time I'm seeing

Why is a dynamic object valid to set to a class in typescript

由 六月ゝ 毕业季﹏ 提交于 2019-12-10 18:36:30
问题 I have played a little bit with typescript and found this: class Greeter { e: number; p: boolean = true; } const xxx = new Greeter(); // true console.log(xxx instanceof Greeter); const xxx2: Greeter = { e: 1, p: true }; // <--- 1. why is this valid? console.log(xxx2 instanceof Greeter); // false const xxx3: Greeter = Object.setPrototypeOf({ e2: 1 }, Greeter.prototype); // <-- 2. no warning? console.log(xxx2 instanceof Greeter); // true So my Question is: Why is it valid in typescript to

instanceof use for multiple types

由 元气小坏坏 提交于 2019-12-10 16:47:28
问题 I am writing a TypeChecker for MiniJava and ExpOp needs to check if both of the entered expressions are of Integer to use plus, minus, times. How can I write a line of code inside an if statement that includes both expressions and checks if both of them are instances of ( instanceof ) Integer ? This is what I have now: n.e1.accept(this) n.e2.accept(this) instanceof Integer Appreciate your help. 回答1: instanceof is a binary operator: it can only have two operands. The best solution for your

Instanceof fails in iframe [duplicate]

由 蓝咒 提交于 2019-12-10 16:21:31
问题 This question already has answers here : instanceof operator fails when passing an object through windows (1 answer) Why are myarray instanceof Array and myarray.constructor === Array both false when myarray is in a frame? (2 answers) Closed last year . The following code returns true . console.log(document.createElement('script') instanceof Element); Doing the same in an <iframe> context returns false : let iframe = document.querySelector('iframe'); iframe = iframe.contentDocument || iframe

014-Java多态-instanceof关键字

由 ▼魔方 西西 提交于 2019-12-10 14:18:59
目录 多态定义 多态的前提 格式 多态的好处 多态访问成员变量的两种方式 在多态的代码当中，成员方法的访问规则 引用类型转换 向上转型 向下转型 为什么要转型 instanceof关键字 感谢关注 多态是继封装、继承之后，面向对象的第三大特性。 生活中，比如跑的动作，小猫、小狗和大象，跑起来是不一样的。再比如飞的动作，昆虫、鸟类和飞机，飞起来也是不一样的。可见，同一行为，通过不同的事物，可以体现出来的不同的形态。多态，描述的就是这样的状态。 多态定义 多态： 是指同一行为，具有多个不同表现形式。 多态的前提 1.继承或者实现 2. 方法的重写，不重写是无意义的 3. 父类引用指向子类对象 格式 格式： 父类名称 对象名 = new 子类名称(); 或者： 接口名称 对象名 = new 实现类名称(); 父类类型 变量名 = new 子类对象； 变量名.方法名(); 父类类型：指子类对象继承的父类类型，或者实现的父接口类型。 当使用多态方式调用方法时，首先检查父类中是否有该方法，如果没有，则编译错误；如果有，执行的是子类重写后方法。 多态的好处 实际开发的过程中，父类类型作为方法形式参数，传递子类对象给方法，进行方法的调用，更能体现出多态的扩展、性与便利。 多态访问成员变量的两种方式 1. 直接通过对象名称访问成员变量：看等号左边是谁，优先用谁，没有则向上找。 2.

Haskell instanceof analogue?

由 ぐ巨炮叔叔 提交于 2019-12-10 13:44:07
问题 I am new to Haskell, so my question is probably stupid. I want a function show2 :: (Show a) => a -> String which would return show a for any a , but a if a is itself String . How can I implement it? P.S. it is great if this function is already implemented somewhere, but I still want to see an example of the implementation. 回答1: You can do this with this piece of dirty and dangerous code: class Showable a where show2 :: a -> String instance Showable String where show2 = id instance (Show a) =>

How to Determine Type of Child Class from Method of Parent Class without Instanceof in Java

由 不打扰是莪最后的温柔 提交于 2019-12-10 12:07:36
问题 The following code runs, but my implementation violates SOLID principles. I'm hoping someone can help me redesign my code so that it follows SOLID principles, particularly by avoiding the use of instanceof . I have a parent class, Parent , with three child classes: Element , Container , and Wrapper . Element simply holds an integer, like a math scalar. Container has a parent array, Parent[] contents , which may be any of the child classes, like a math vector. It can be a vector of scalars

Usage of instanceof in a generic method

由 为君一笑 提交于 2019-12-10 11:33:57
问题 I started to learn generics today, but this is somelike weird for me: I have a generic method: public<T> HashMap<String, T> getAllEntitySameType(T type) { System.out.println(type.getClass()); HashMap<String, T> result = null; if(type instanceof Project) { System.out.println(type.toString()); System.out.println("Yes, instance of Project;"); } if(type instanceof String) { System.out.println(type.toString()); System.out.println("Yes, instance of String;"); } this.getProjects(); return result; }
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