functionmyFunction() { x = document.getElementById("demo") x.innerHTML = numbers.map(Math.sqrt); } 输出结果为: 2,3,4,5 尝试一下 » 定义和用法 map() 方法返回一个新数组,数组中的元素为原始数组元素调用函数处理后的值。 map() 方法按照原始数组元素顺序依次处理元
// 将数组中的每个数字乘以 2 const numbers = [1, 2, 3, 4]; const doubled = numbers.map(function(num) { return num * 2; }); console.log(doubled); // 输出: [2, 4, 6, 8] // 使用箭头函数简化代码 const doubledWithArrow = numbers.map(num => num * 2); console.log(double...
keyValArr=[...map]//将map转换成数组(忽略key取value)arr=[...map.values()]//将map转回对象obj=Object.fromEntries(map)//将键值对数组转换回对象obj=Object.fromEntries(keyValArr)//将数组转为Set 若数组存在重复元素将自动去重let set=newSet(arr)//将set转换回数组arr=[...set] arr=Array.from(set...
In the above code, a callback function is provided to theArray.map()method, which is executed for each object in the array. During each iteration, an array is returned containing the key and value for each object, resulting in an array of key-value pairs: constusers=[{name:'John Doe'...
一句话概括:for in是遍历(object)键名,for of是遍历(array)键值——for of 循环用来获取一对键值对中的值,而 for in 获取的是 键名。 for in 循环出的是key(并且key的类型是string),for of 循环出的是value。 for of 是es6引新引入的特性,修复了es5引入的for in 的不足。
push(array); }); return Object.keys(groups).map(function(group){ return groups[group] }) }; //使用groupBy函数 let result=groupBy(datas,function(item){ return item.name; //根据name分组 }); console.log(result); 运行结果为: call()和apply() 这两个函数都能改变一个函数中的this对象的...
V8里面所有的数据类型的根父类都是Object,Object派生HeapObject,提供存储基本功能,往下的JSReceiver用于原型查找,再往下的JSObject就是JS里面的Object,Array/Function/Date等继承于JSObject。左边的FixedArray是实际存储数据的地方。推荐看原文《从Chrome源码看JS Object的实现》 在创建一个JSObject之前,会先把读到的Objec...
* @param callback [function] 回调函数; * @param context [object] 上下文; */ Array.prototype.myMap = function myMap(callback,context){ context = context || window if('map' in Array.prototype) { return this.map(callback, context) } //IE6-8下自己编写回调函数执行的逻辑 let newAry =...
The initial geographical centerpoint of the map. If center is not specified in the constructor options, Mapbox GL JS will look for it in the map's style object. If it is not specified in the style, either, it will default to [0, 0] Note: Mapbox GL uses longitude, latitude coordinat...
map() calls the helper function for the first item in the array. It passes three parameters to the function: The value of the first array item. The index of the item (optional parameter). The original array object (optional parameter). The function runs to completion and returns a value ...