var total = [ 0, 1, 2, 3 ].reduce(( acc, cur ) => {
 return acc + cur
}, 0);
console.log(total) // 6

var array = [[1, 2], [3, 4], [5, 6]].reduce(( acc, cur ) => {
  return acc.concat(cur)
}, []);
console.log(array) // [ 0, 1, 3, 4, 5, 6 ]

let names = ['tom', 'jim', 'jack', 'tom', 'jack'];
const countNames = names.reduce((allNames, name) => {
 if (name in allNames) {
  allNames[name] ++;
 }
 else {
  allNames[name] = 1;
 }
 return allNames;
}, {});

console.log(countNames) // { tom: 2, jim: 1, jack: 2 }

const arraySum = (arr, val) => arr.reduce((acc, cur) => {
  return cur == val "color: #ff0000">数组去重


1.方法一


let arr = [1, 2, 1, 2, 3, 5, 4, 5, 3, 4, 4, 4, 4];
let result = arr.sort().reduce((init, current) => {
  if (init.length === 0 || init[init.length - 1] !== current) {
    init.push(current);
  }
  return init;
}, []);
console.log(result); //[1,2,3,4,5]


2.方法二


当然，对于数组去重，也可以直接使用es6的…[拓展运算符] + Set 实现：


// console.log(...new Set([1,2,3,4,5,2,4,1]))
const dedupe = (array) => {
  return Array.from(new Set(array));
}
console.log(dedupe([1, 1, 2, 3])) //[1,2,3]


总结
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