你好，JS生成重复字符串再新ES标准中很简单，只需使用字符串的repeat方法就可以实现：var str = 'Test'str = str.repeat(3)// TestTestTest但是这个方法是ES2015中新增的标准，在老规范中是无法被兼容的。但是，我们也可以用其他的方法实现：var str = 'Test'str = new Array(3 + 1).join(str)// TestTestTest另外，使用最原始的循环遍历也是可以的：var str = 'Test'for (var i = 3 - 1ii--) {str += 'Test'}// str =>TestTestTest因此，我们可以得到一个兼容的repeat方法：String.prototype.repeat = String.prototype.repeat || function(num) {return new Array(num + 1).join(this)}'Test'.repeat(3)// TestTestTest好了，就这么多了，希望能解决你的问题。

经过babel的转换后

其实原理就是字符串拼接。所以如果${}中不是字符串，则会类型转换成字符串

标签模板

标签模板更多的是用来自定义拼接规则的。

手写startsWith、endsWite、includes

v8 js源码中的startsWith

includes

repeat方法返回一个新字符串，表示将原字符串重复n次。

如果repeat的参数是负数或者Infinity，会报错。

v8 js源码中的repeat

fromCharCode不能识别码点大于0xFFFF的字符。需要使用fromCodePoint

同样charCodeAt无法识别大于0xFFFF的字符 需要使用codePointAt

const List = [{"end_date":"2022-02-10","end_seconds":1644488295.0,"end_total_seconds":0,"first_heart_beat_time":"2022-02-10 18:08:34","id":10319,"last_heart_beat_time":"2022-02-10 18:18:15","scanner_id":167,"start_date":"2022-02-10","start_seconds":1644487714.0,"start_total_seconds":581},{"end_date":"2022-02-11","end_seconds":1644550497.0,"end_total_seconds":0,"first_heart_beat_time":"2022-02-11 11:19:08","id":10338,"last_heart_beat_time":"2022-02-11 11:34:57","scanner_id":167,"start_date":"2022-02-11","start_seconds":1644549548.0,"start_total_seconds":949},{"end_date":"2022-02-11","end_seconds":1644558220.0,"end_total_seconds":0,"first_heart_beat_time":"2022-02-11 11:48:41","id":10339,"last_heart_beat_time":"2022-02-11 13:43:40","scanner_id":167,"start_date":"2022-02-11","start_seconds":1644551321.0,"start_total_seconds":6899},{"end_date":"2022-02-11","end_seconds":1644558820.0,"end_total_seconds":0,"first_heart_beat_time":"2022-02-11 13:53:40","id":10343,"last_heart_beat_time":"2022-02-11 13:53:40","scanner_id":167,"start_date":"2022-02-11","start_seconds":1644558820.0,"start_total_seconds":0},{"end_date":"2022-02-11","end_seconds":1644563620.0,"end_total_seconds":0,"first_heart_beat_time":"2022-02-11 14:03:41","id":10344,"last_heart_beat_time":"2022-02-11 15:13:40","scanner_id":167,"start_date":"2022-02-11","start_seconds":1644559421.0,"start_total_seconds":4199},{"end_date":"2022-02-11","end_seconds":1644586551.0,"end_total_seconds":0,"first_heart_beat_time":"2022-02-11 15:55:51","id":10350,"last_heart_beat_time":"2022-02-11 21:35:51","scanner_id":167,"start_date":"2022-02-11","start_seconds":1644566151.0,"start_total_seconds":20400},{"end_date":"2022-02-13","end_seconds":1644759468.0,"end_total_seconds":0,"first_heart_beat_time":"2022-02-13 14:47:48","id":10410,"last_heart_beat_time":"2022-02-13 21:37:48","scanner_id":167,"start_date":"2022-02-13","start_seconds":1644734868.0,"start_total_seconds":24600},{"end_date":"2022-02-14","end_seconds":1644846304.0,"end_total_seconds":0,"first_heart_beat_time":"2022-02-14 10:15:05","id":10430,"last_heart_beat_time":"2022-02-14 21:45:04","scanner_id":167,"start_date":"2022-02-14","start_seconds":1644804905.0,"start_total_seconds":41399},{"end_date":"2022-02-15","end_seconds":1644911999.0,"end_total_seconds":0,"first_heart_beat_time":"2022-02-15 15:30:00","id":10468,"last_heart_beat_time":"2022-02-15 15:59:59","scanner_id":167,"start_date":"2022-02-15","start_seconds":1644910200.0,"start_total_seconds":1799},{"end_date":"2022-02-15","end_seconds":1644932084.0,"end_total_seconds":0,"first_heart_beat_time":"2022-02-15 19:44:44","id":10472,"last_heart_beat_time":"2022-02-15 21:34:44","scanner_id":167,"start_date":"2022-02-15","start_seconds":1644925484.0,"start_total_seconds":6600},{"end_date":"2022-02-16","end_seconds":1645020217.0,"end_total_seconds":0,"first_heart_beat_time":"2022-02-16 15:13:37","id":10491,"last_heart_beat_time":"2022-02-16 22:03:37","scanner_id":167,"start_date":"2022-02-16","start_seconds":1644995617.0,"start_total_seconds":24600},{"end_date":"2022-02-17","end_seconds":1645089245.0,"end_total_seconds":0,"first_heart_beat_time":"2022-02-17 14:59:06","id":10521,"last_heart_beat_time":"2022-02-17 17:14:05","scanner_id":167,"start_date":"2022-02-17","start_seconds":1645081146.0,"start_total_seconds":8099}]

        const newArray = []

        List.forEach(item =>{

            // 第一次循环,repeat定义repet,基于find浅拷贝特性,操作repeat会影响到newArray

            // 循环开始,find的条件不成立,就会push一个新对象{data: item.start_date,times: [item]}进去

            // 检索条件要注意,find的核对条件需要准确

            // 第二次循环,find条件成立,则走else

            const repeat = newArray.find(res =>res.data === item.start_date)

            if (!repeat) {

                newArray.push({

                    data: item.start_date,

                    times: [item]

                })

            } else {

                // 避免循环紊乱,不用item.times.push(item),选用repeat.times.push(item)

                repeat.times.push(item)

            }

        })

打印数据后可以看到，已经将数据成功照相同时间的start_date重新管理

如果前端需要解决时间归类当天的用户多部操作但是后端没处理，就可以用forEach+find的方法处理

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