Learn how to use array reduction to create functional pipelines by composing arrays of functions. const increase = (input) => { return input + 1; } const decrease = (input) => { return input - 1; } const double = (input) => { return input * 2; }…
Learn a few advanced reduction patterns: flatten allows you to merge a set of arrays into a single array, the dreaded flatmap allows you to convert an array of objects into an array of arrays which then get flattened, and reduceRight allows you to in…
Take away: Always check you ruturn the accumulator Always pass in the inital value var data = ["vote1", "vote2", "vote1", "vote2"]; var reducer = function(acc, value){ if(acc[value]){ acc[value] = acc[value] + 1; }e…
Sometimes we need to turn arrays into new values in ways that can't be done purely by passing an accumulator along with no knowledge about its context. Learn how to reduce an array of numbers into its mathematical mean in a single reduce step by usin…
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: <!--Add by oscar999--> <!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.0 Transitional//EN"&g…
题目: 1.得到 3000 到 3500 之内工资的人. 2.增加一个年龄的字段,并且计算其年龄. 3.打印出每个人的所在城市 4.计算所有人的工资的总和. 测试数据: function getData() { var arr = [{ id: 1, name: 'ohzri', birth: '1999.09.09', city: '湖北', salary: 9379 }, { id: 2, name: 'rqgfd', birth: '1999.10.28', city: '湖北', sal…
一文搞懂JavaScript数组中最难的数组API--reduce() 前面我们讲了数组的一些基本方法,今天给大家讲一下数组的reduce(),它是数组里面非常重要也是比较难的函数,那么这篇文章就好好给大家介绍下reduce函数. 还是老样子,我们直接在应用中学习,直接上例子.让我们先定义一个包含几个对象的数组,注意观察下这个数组,可以看到里面有两个对象的age都是30.(下面会用到) // 一个包含几个人物对象的数组. const people = [ { name: "John",…
一直对map.foreach.reduce这些函数很是生疏,今天看underscorejs时好好研究了一下,一研究我就更懵了,这不是一样嘛,都是遍历,所以我就去知乎找了一下,整理出了比较好的几个说法. 假设我们有一个数组,每个元素是一个人.你面前站了一排人. foreach 就是你按顺序一个一个跟他们做点什么,具体做什么,随便: people.forEach(function (dude) { dude.pickUpSoap();}); map 就是你手里拿一个盒子(一个新的数组),一个一个叫他…
案例: var scoresTable=[ {id:11,name:"小张",score:80}, {id:22,name:"小王",score:95}, {id:33,name:"小李",score:50}, {id:44,name:"小刘",score:65}, {id:55,name:"小徐",score:84} ] 1.快速获取最高score值(采用map,Max.sum和apply) var sc…
Callback functions are extremely important in Javascript. They’re pretty much everywhere. Originally coming from a more traditional C/Java background I had trouble with this (and the whole idea of asynchronous programming), but I’m starting to get th…