如果这个参数为空, "undefined" 会传递给 "this" 值 技术细节 返回值:返回符合测试条件的第一个数组元素值,如果没有符合条件的则返回undefined。 JavaScript 版本:ECMAScript 6 更多实例 实例 返回符合大于输入框中数字的数组索引值: varages=[4,12,16,20];functioncheckAdult(age){returnage>=document.getElemen...
log(username); //returns Hunter; } checkVars() //executes function; function checkVars(){ var username; console.log(username); //returns undefined username = "Hunter"; console.log(username); //returns Hunter; } checkVars() //executes function; Listing 3-7Variables Are Hoisted When They A...
Object.defineProperty(obj,"firstKey", { value:"hello world",// 属性的值,默认为undefined writable: true,// 是否可修改,默认为false enumerable: true,// 是否可枚举(遍历),默认为false configurable: true// 表示对象的属性是否可以被删除,以及除 value 和 writable 特性外的其他特性是否可以被修改。 });...
thrownewError('rate in heart is undefined') } // Assume the caller wants to pass in a callback to receive the current frog's weight and height that he or she has set // previously so they can calculate the heart object on the fly. Useful for loops of collections if (typeof heart ...
undefined 但是,如果省略var关键字,就不再声明变量,而是初始化它。它将返回一个ReferenceError并停止脚本的执行。 代码语言:javascript 代码运行次数:0 运行 AI代码解释 //在声明变量之前尝试使用它 console.log(x); //没有var的变量赋值 x = 100; 输出: 代码语言:javascript 代码运行次数:0 运行 AI代码解释 ...
apiKey String |null |undefined Since: ArcGIS Maps SDK for JavaScript 4.20 An authorization string used to access a resource or service. API keys are generated and managed in the portal. An API key is tied explicitly to an ArcGIS account; it is also used to monitor service usage. Setting...
* | undefined The removed item if present in the collection, undefined otherwise. Example // Removes the layer at index 4 of the map map.layers.removeAt(4); removeHandles Inherited Method removeHandles(groupKey) Inherited from Accessor Since: ArcGIS Maps SDK for JavaScript 4.25 Removes...
+t,sampleRate:100,tags:n,data:{baseData:{ver:2}},ver:undefined,seq:"1",aiDataContract:undefined}}var n,i,t,a,y=-1,T=0,S=["js.monitor.azure.com","js.cdn.applicationinsights.io","js.cdn.monitor.azure.com","js0.cdn.applicationinsights.io","js0.cdn.monitor.azure.com","js2....
数组实例的find()用于找出第一个符合条件的数组元素。它的参数是一个回调函数,所有数组元素依次遍历该回调函数,直到找出第一个返回值为true的元素,然后返回该元素,否则返回undefined。 find() 方法返回通过测试(函数内判断)的数组的第一个元素的值。find() 方法为数组中的每个元素都调用一次函数执行: ...
Exposer.first(); // Output: This is a method I want to expose!Exposer.second(); // Output: Inside a private method!Exposer.methodToExpose; // undefined 尽管这看起来更简洁,但一个明显的缺点是无法引用私有方法。这可能会带来单元测试挑战。同样,...