这篇文章给大家带来的内容是关于javascript中reduce的用法总结(附代码) ,有一定的参考价值,有需要的朋友可以参考一下,希望对你有所帮助。
最近经常在项目中经常看到别人用reduce处理数据,很是牛掰,很梦幻, 不如自己琢磨琢磨。
array.reduce(function(total, currentValue, currentIndex, arr), initialValue); /* total: 必需。初始值, 或者计算结束后的返回值。 currentValue: 必需。当前元素。 currentIndex: 可选。当前元素的索引; arr: 可选。当前元素所属的数组对象。 initialValue: 可选。传递给函数的初始值,相当于total的初始值。 */
const arr = [12, 34, 23]; const sum = arr.reduce((total, num) => total + num); <!-- 设定初始值求和 --> const arr = [12, 34, 23]; const sum = arr.reduce((total, num) => total + num, 10); // 以10为初始值求和 <!-- 对象数组求和 --> var result = [ { subject: 'math', score: 88 }, { subject: 'chinese', score: 95 }, { subject: 'english', score: 80 } ]; const sum = result.reduce((prev, cur) => prev + cur.score, 0); const sum = result.reduce((prev, cur) => prev + cur.score, -10); // 总分扣除10分
const a = [23,123,342,12]; const max = a.reduce(function(pre,cur,inde,arr){return pre>cur?pre:cur;}); // 342
<!-- 比如生成“老大、老二和老三” --> const objArr = [{name: '老大'}, {name: '老二'}, {name: '老三'}]; const res = objArr.reduce((pre, cur, index, arr) => { if (index === 0) { return cur.name; } else if (index === (arr.length - 1)) { return pre + '和' + cur.name; } else { return pre + '、' + cur.name; } }, '');
const str = 'sfhjasfjgfasjuwqrqadqeiqsajsdaiwqdaklldflas-cmxzmnha'; const res = str.split('').reduce((prev, cur) => {prev[cur] ? prev[cur]++ : prev[cur] = 1; return prev;}, {});
<!-- 按照一定的规则转成数组 --> var arr1 = [2, 3, 4, 5, 6]; // 每个值的平方 var newarr = arr1.reduce((prev, cur) => {prev.push(cur * cur); return prev;}, []);
<!-- 按照id 取出stream --> var streams = [{name: '技术', id: 1}, {name: '设计', id: 2}]; var obj = streams.reduce((prev, cur) => {prev[cur.id] = cur; return prev;}, {});
<!-- 各科成绩占比重不一样, 求结果 --> var result = [ { subject: 'math', score: 88 }, { subject: 'chinese', score: 95 }, { subject: 'english', score: 80 } ]; var dis = { math: 0.5, chinese: 0.3, english: 0.2 }; var res = result.reduce((prev, cur) => dis[cur.subject] * cur.score + prev, 0); <!-- 加大难度, 商品对应不同国家汇率不同,求总价格 --> var prices = [{price: 23}, {price: 45}, {price: 56}]; var rates = { us: '6.5', eu: '7.5', }; var initialState = {usTotal:0, euTotal: 0}; var res = prices.reduce((prev1, cur1) => Object.keys(rates).reduce((prev2, cur2) => { console.log(prev1, cur1, prev2, cur2); prev1[`${cur2}Total`] += cur1.price * rates[cur2]; return prev1; }, {}), initialState); var manageReducers = function() { return function(state, item) { return Object.keys(rates).reduce((nextState, key) => { state[`${key}Total`] += item.price * rates[key]; return state; }, {}); } }; var res1= prices.reduce(manageReducers(), initialState);
var arr = [[1, 2, 8], [3, 4, 9], [5, 6, 10]]; var res = arr.reduce((x, y) => x.concat(y), []);
const hash = {}; chatlists = chatlists.reduce((obj, next: Object) => { const hashId = `${next.topic}_${next.stream_id}`; if (!hash[hashId]) { hash[`${next.topic}_${next.stream_id}`] = true; obj.push(next); } return obj; }, []);
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