这就是@Optional()装饰器的作用。@Optional()装饰器告诉 Angular 的依赖注入系统,这个依赖是可选的,如果找不到这个依赖,那么就注入null。 下面是一个使用@Optional()的例子: import { Optional } from '@angular/core'; constructor(@Optional() private userService: UserService) { } 在这个例子中,如果UserSe...
(5). 可选参数(optional parameters) JavaScript: JS中所有的参数都是可选参数。这可以理解为JS的特性也可以说是设计缺陷,毕竟有时候漏传参数又不报错容易导致各种问题。 Dart: 在Dart中,常规的参数都是必传的,而命名参数和位置参数(positional parameter)都可以是可选参数。当然方法体中需要增加容错逻辑,已防止可...
“Math is not a function.”:“Math不是一个函数”, “Missing ‘new’ prefix when invoking a constructor.”:“此处缺少了’new’”, “Missing radix parameter.”:“缺少参数”, “Implied eval is evil. Pass a function instead of a string.”:“传递一个函数,而不是一个字符串”, “Bad invocat...
In this second example, the optional extent parameter is also included in the constructor. require([ "esri/map", "esri/geometry/Extent", ... ], function(Map, Extent, ... ) { var map = new Map("mapDiv", { extent: new Extent(-124.71, 31.89, -113.97, 42.63) }); ...}); This...
class Car { constructor() { // 绑定 sayBye 而不是 sayHi 来展示差异 this.sayBye = this.sayBye.bind(this); } sayHi() { console.log(`Hello from ${this.name}`); } sayBye() { console.log(`Bye from ${this.name}`); } get name() { return "Ferrari"; } } class Bird { get ...
import javascript from SimpleParameter res, DataFlow::Node resNode, MethodCallExpr send where res.getName() = "res" and resNode = DataFlow::parameterNode(res) and resNode.getASuccessor+() = DataFlow::valueNode(send.getReceiver()) and send.getMethodName() = "send" select send Note that...
Optional parameters may be specified in the optional third parameter for loginImplicitGrant. This parameter accepts an object with key/value pairs. Supported properties:state - An arbitrary string used to associate a login request with a login response. This value will be provided in the state ...
Portal Constructor new Portal(properties) Parameter properties Object optional See the properties for a list of all the properties that may be passed into the constructor. Property Overview Any properties can be set, retrieved or listened to. See the Watch for changes topic. Hide inherited ...
Thelocaleargument ofnew TimeAgo(locale)constructor is matched against the list of added languages, and the first matching one is used. For example, locales"en-US"and"en-GB"both match"en"language. If none of the added languages match thelocale, the "default language" is used. If the "defa...
Example 1: Introducing an optional parameter A new parameter i2 is extracted as an optional parameter. The new parameter is initialized in the body of calculate_sum(i) and the call of calculate_sum(i) in show_sum() is not changed. See Choosing the parameter type (optional) below. Before...