Javascript: Linq.js:返回数组

Question

我是Linq.js新手，正在尝试获取json字符串的一个子集。我的Json字符串如下: eventJSON：

[{"EventID": "1", "Description": "Hello World", "EventTime": "16123456000"}, 
{"EventID": "2", "Description": "Carpe Diem", "EventTime": "16123656000"}, 
{"EventID": "3", "Description": "Desc3", "EventTime": "16123656000"}] 

我有一个遍历这个json的函数，并尝试根据eventtime值返回一个子集。THe代码如下：

videoPlayer.on('playtime', function (pts) {
    var pts = 16123656000;

    if (eventJSON != null) {
        var _resultArray = Enumerable.From(eventJSON).Select(function (eventrecord) { return Number(eventrecord.EventTime) == Number(pts); }).ToArray();
        if (_resultArray.length > 0) {
            _resultArray.forEach(function (item, index, array) {
                console.log(item.EventTime);
            }
            )                
        }                
    }
});

这似乎不起作用。如何将json的子集作为数组获取并遍历它们？

Answer 1

你不需要linq.js来做这件事。只需使用Array.filter即可

let data = [{"EventID": "1", "Description": "Hello World", "EventTime": "16123456000"}, 
{"EventID": "2", "Description": "Carpe Diem", "EventTime": "16123656000"}, 
{"EventID": "3", "Description": "Desc3", "EventTime": "16123656000"}];

let pts = 16123656000;

let filtered = data
  .filter(x => +x.EventTime === pts);
filtered.forEach(x => console.log(x.EventTime));

对于第二个需求，您可以使用Array.sort、Array.find或Array.reduce

//find latest with <= pts Variant 1
//sort descending and find the first element that meets the condition
let latest = data
  .sort((a,b) => +b.EventTime - +a.EventTime)
  .find(x => +x.EventTime <= pts)

//Variant 2
//filter all elements meeting the condition, sort descending 
//and take the first element
let latest = data
  .filter(x => +x.EventTime <= pts)
  .sort((a,b) => +b.EventTime - +a.EventTime)[0]

//Variant 3
//using reduce and search for the maximum meeting the condition
let latest = data.reduce((a, c) => {
  if (+c.EventTime > pts) return a;
  if (!a) return c;
  return +a.EventTime > +c.EventTime ? a : c;
  }, undefined);