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[Javascript] Advanced Reduce: Flatten, Flatmap and ReduceRight

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…

[Javascript] Advanced Reduce: Common Mistakes

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…

[Javascript] Advanced Reduce: Additional Reducer Arguments

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…

[Javascript] Advanced Reduce: Composing Functions with Reduce

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; }…

JavaScript中reduce()方法

原文  http://aotu.io/notes/2016/04/15/2016-04-14-js-reduce/   JavaScript中reduce()方法不完全指南 reduce() 方法接收一个函数作为累加器,数组中的每个值(从左到右)开始缩减,最终为一个值,是ES5中新增的又一个数组逐项处理方法,那reduce方法跟foreach.map等数组方法又有啥区别呢. arr.reduce(callback[, initialValue]) - More From MDN callback…

JavaScript: Advanced

DOM 1. 节点 getElementsByName方法 <!DOCTYPE HTML> <html> <head> <script type="text/javascript"> function getnum(){ var mynode = document.getElementsByName("myt"); alert(mynode.length); } </script> </head>…

[Javascript] Advanced Console Log Arguments

Get more mileage from your console output by going beyond mere string logging - log entire introspectable objects, log multiple items in one call, and apply C-Style string substitution to make the console work for you. // Can accept multi args consol…

[Javascript] Introducing Reduce: Common Patterns

Learn how two common array functions - map() and filter() - are syntactic sugar for reduce operations. Learn how to use them, how to compose them, and how using reduce can give you a big performance boost over composing filters and maps over a large…

javascript之reduce()方法的使用

以前看到reduce方法,总是看得我头皮发麻,今天无意间又遇到他了,于是学习了下,接触之后,觉得这个方法还挺好用的,在很多地方都可以派上用场,比如,数组中元素求和.数组去重.求数组中的最大值或最小值等等都可以用到它. reduce() 方法接收一个函数作为累加器,数组中的每个值(从左到右)开始缩减,最终计算为一个值. 语法:array.reduce(function(total, currentValue, currentIndex, arr), initialValue) 可以看出它接收一个回…

JavaScript map reduce

23333333333333 map var s = []; for(let i=0;i<10;i++){ s.push(i); } function pow(x){ return x*x; } console.log(s.map(pow)); console.log(s.map(String)); reduce()方法接收一个函数作为累加器(accumulator),数组中的每个值(从左到右)开始缩减,最终为一个值. var arr = [10,20,30,40,50]; var reduce…