[Javascript + rxjs] Using the map method with Observable

Like an array, Observable has a map method that allows us to transform a sequence into a new Observable. var Observable = Rx.Observable; //Create click events by Observable var clicks = Observable.fromEvent(button, 'click'); var points = clicks.map(f…

[Javascript] The Array map method

One very common operation in programming is to iterate through an Array's contents, apply a function to each item, and create a new array containing the results. For example, let's say you wanted to loop through an array of stock objects and select o…

Javascript中Array.prototype.map()详解

map 方法会给原数组中的每个元素都按顺序调用一次 callback 函数.callback 每次执行后的返回值组合起来形成一个新数组. callback 函数只会在有值的索引上被调用:那些从来没被赋过值或者使用 delete 删除的索引则不会被调用. 在我们日常开发中,操作和转换数组是一件很常见的操作,下面我们来看一个实例: 复制代码代码如下: var desColors = [], srcColors = [ {r: 255, g: 255, b: 255 }, // W…

百度地图JavaScript API经纬度查询-MAP

百度地图JavaScript API经纬度查询-MAP-ABCDEFGHIJKMHNOPQRSTUVWXYZ: 搜索:<input type="text" size="20" name="keyword" id="keyword" /> <input type="submit" value="提交" onclick="MblogDotccMap(documen…

[Javascript + rxjs] Introducing the Observable

In this lesson we will get introduced to the Observable type. An Observable is a collection that arrives over time. Observables can be used to model events, asynchronous requests, and animations. Observables can also be transformed, combined, and con…

[RxJS] Add debug method to Observable in TypeScript

Observable.prototype.debug = function(message: any) { return this.do( (next) => { if(!environment.production) { console.log(message, next); } }, (err) => { if(!environment.production) { console.error(message, err) } }, () => { if(!environment.pro…

[Javascript + rxjs] Simple drag and drop with Observables

Armed with the map and concatAll functions, we can create fairly complex interactions in a simple way. We will use Observable to create a simple drag and drop example with basic DOM elements. <!DOCTYPE html> <html> <head lang="en"…

android 平台 java和javascript 通信问题 A WebView method was called on thread 'JavaBridge'.

java.lang.RuntimeException: java.lang.Throwable: A WebView method was called on thread 'JavaBridge'. All WebView methods must be called on the same thread 之前的 android4.4版本的代码跑没有问题,到了5.0出了这个问题.查询百度.解决方法: //4.4之前版本调用函数 public void sendToJs(){ try { M…

[RxJS] Implement the `map` Operator from Scratch in RxJS

While it's great to use the RxJS built-in operators, it's also important to realize you now have the knowledge to write them by yourself if needed. The mapoperator turns out to be a simple MapSubscriber which takes a function and applies it to the va…

[RxJS] Use RxJS concatMap to map and concat high order observables

Like switchMap and mergeMap, concatMap is a shortcut for map() followed by a concatAll(). In this lesson we will explore this RxJS operator and its properties. const clickObservable = Rx.Observable .fromEvent(document, 'click'); function performReque…

[RxJS] Use RxJS mergeMap to map and merge high order observables

Like RxJS switchMap() is a shortcut for map() and switch(), we will see in this lesson how mergeMap() is a shortcut for map() and mergeAll(), and learn its arguments for customised behavior. const clickObservable = Rx.Observable .fromEvent(document,…

RxJS——可观察的对象（Observable）

可观察的(Observable) 可观察集合(Observables)是多值懒推送集合.它们填补了下面表格的空白: SINGLE MULTIPLE Pull Function Iterator Push Promise Observable 举个例子,下面是一个可观察对象,当它被订阅的时候立即推送值 1,2,3,并且值 4 在订阅调用之后的一秒传递过去,然后完成: import { Observable } from 'rxjs'; const Observable = new Observab…

JavaScript高阶函数 map reduce filter sort

本文是笔者在看廖雪峰老师JavaScript教程时的个人总结高阶函数一个函数就接收另一个函数作为参数,这种函数就称之为高阶函数 1.高阶函数之map: 此时我们有一个数组和一个接受一个参数并返回一个数的函数.我们需要把这个数组的每一个值在这个函数上走一遍,从而得到一个新数组.此时就需要map了 var a = [1,2,3,4,5,6]; var b = [] var fu…

[RxJS] Transformation operator: map and mapTo

We made our first operator called multiplyBy, which looks a bit useful, but in practice we don't need it because it's too specific: it only does simple multiplication on numbers. In this lesson we will see how the map() operator is useful for any cal…

JavaScript数组forEach()、map()、reduce()方法

1. js 数组循环遍历. 数组循环变量,最先想到的就是 for(var i=0;i<count;i++)这样的方式了. 除此之外,也可以使用较简便的forEach 方式 2. forEach 函数. Firefox 和Chrome 的Array 类型都有forEach的函数.使用如下:  <!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.0 Transitional//EN"&g…

JavaScript高阶函数map/reduce、filter和sort

map() 举例说明,比如我们有一个函数f(x)=x²,要把这个函数作用在一个数组[1,2,3,4,5,6,7,8,9]上. 由于map()方法定义在JavaScript的Array中,我们调用Array的map()方法,传入我们自己的函数,就得到了一个新的Array作为结果: function pow(x) { return x*x; } var arr = [1,2,3,4,5,6,7,8,9]; arr.map(pow);//[1,4,9,16,25,36,49,64,81] map()传…

关于Javascript的forEach 和 map

本篇博客转载自 https://blog.fundebug.com/2018/02/05/map_vs_foreach/ 如果你已经有使用JavaScript的经验,你可能已经知道这两个看似相同的方法:Array.prototype.map()和Array.prototype.forEach(). 那么,它们到底有什么区别呢? 定义我们首先来看一看MDN上对Map和ForEach的定义: forEach(): 针对每一个元素执行提供的函数(executes a provided functio…

【前端_js】javascript中数组的map()方法

数组的map()方法用于遍历数组,每遍历一个元素就调用回调方法一次,并将回调函数的返回结果作为新数组的元素,被遍历的数组不会被改变. 语法:let newAarray = arr.map(function callback(currentValue, index, array) { // Return element for newArray } 示例: let numbers = [1, 5, 10, 15]; let doubles = numbers.map((x) => { return…

[ES2019] Use JavaScript ES2019 flatMap to Map and Filter an Array

ES2019 introduces the Array.prototype.flatMap method. In this lesson, we'll investigate a common use case for mapping and filtering an array in a single iteration. We'll then see how to do this using Array.prototype.reduce, and then refactor the code…

javascript中数组的map方法

map方法原型:array1.map(callbackfn[, thisArg]) 参数: array1,必选. 一个数组对象.该函数一般用于数组对象 callbackfn,必选. 最多可以接受三个参数的函数. 对于数组中的每个元素,map 方法都会调用 callbackfn 函数一次. thisArg,可选. callbackfn 函数中的 this 关键字可引用的对象. 如果省略 thisArg,则 undefined 将用作 this 值. 返回值: 一个新数组,其中的每个元素均为关联的原…

[Javascript] Chaining the Array map and filter methods

Both map and filter do not modify the array. Instead they return a new array of the results. Because both map and filter return Arrays, we can chain these functions together to build complex array transformations with very little code. Finally we can…

用javascript实现java的Map

JavaScript:['1','2','3'].map(parseInt)问题解析

最近碰到了['1','2','3'].map(parseInt)这种看似不起眼陷阱却极大的问题. 这乍一看,感觉应该会输出[1,2,3].但是,实际上并不是我们想的这样.你可以现在打开console,看看输出的结果. 出乎意料结果竟然是[1,NaN,NaN]. 至于为什么是这样,下面一步一步的解释. parseInt() 函数定义和用法 parseInt() 函数可解析一个字符串,并返回一个整数. 语法 parseInt(string, radix) 参数描述 string 必需.要被解析的…

javascript的数组之map()

map()方法创建一个新数组,其结果是该数组中的每个元素都调用一个提供的回调函数后返回的结果.新数组 // ES6 let numbers = [1, 5, 10, 15]; let doubles = numbers.map( x => x ** 2); // doubles is now [1, 25, 100, 225] // numbers is still [1, 5, 10, 15] const numbers = [2, 4, 8, 10]; let halves = number…

JavaScript 数组——filter()、map()、some()、every()、forEach()、lastIndexOf()、indexOf()

filter(): 语法: var filteredArray = array.filter(callback[, thisObject]); 参数说明: callback: 要对每个数组元素执行的回调函数.thisObject : 在执行回调函数时定义的this对象. //过滤掉小于 10 的数组元素: //代码: function isBigEnough(element, index, array) { return (element >= 10); } var filtered = […

《JavaScript》forEach()和map()

js中的forEach()方法只能遍历数组,不能遍历字符串和对象,和$.each()有很多使用上的区别array.forEach(funcion(value,index,arr){},thisValue);value必须:index:元素下标(可选):arr:调用方法的数组thisValue,forEach中,this指代的值 //去除数组中相同的元素 function unique(array){ var arr = [] array.forEach(function(val,key,arrs…

[Python] map Method

Map applies a function to all the items in an input_list Blueprint map(function, list_of_inputs) Most of the times we want to pass all the list elements to a function one-by-one and then collect the output. For instance: items = [1, 2, 3, 4, 5] squar…