Revisit reduce() in js from giving objects in arrays

Suppose there is such an array:

let person = [
     {id: 0, name: "小明"},
     {id: 1, name: "小张"},
     {id: 2, name: "小李"},
     {id: 3, name: "小孙"},
     {id: 1, name: "小周"},
     {id: 2, name: "小陈"},
]

We want to remove objects with duplicate IDs in the array, such as two objects with the same ID of 2——

{id: 2, name: "小李"}和{id: 2, name: "小陈"} （去掉任何一个都可以）

How should we do it? ?

In fact, for array objects, traditional deduplication methods are powerless, and iteration methods such as forEach() and filter() are not easy to use; what can really achieve elegant deduplication is the new addition of ES5 A method - reduce()

reduce() method receives a callback function as the first parameter, and the callback function accepts four parameters, namely:

1. cur => The first value or the result of superposition with subsequent values;

2. next => The next value to be superimposed;

##3. index => Index value;

4. arr => The array itself;

The common method of reduce is to continuously superimpose each element in the array. One item and return it;

let log = console.log.bind(console);
let arr = [1,2,3,4,5,6];
arr = arr.reduce((cur,next) => {     return cur + next;
})
log(arr); // 21

It can be seen that the final result of the above code is 1+2+3+4+5+6 = 21;

In addition, reduce can also receive a second parameter, which is used to declare the type and initial value of cur of the callback function (first parameter);

let log = console.log.bind(console);
let arr = [1,2,3,4,5,6];
arr = arr.reduce((cur,next) => {     return cur + next;
}，0) //指定cur的类型为Number并且初始值为0，当设为1时，最终打印的值为22log(arr); // 21

reduce() is roughly like this. Through this method, we can very elegantly implement deduplication of objects in the array. Let's go back to the array at the beginning of the article:

let log = console.log.bind(console);
let person = [
     {id: 0, name: "小明"},
     {id: 1, name: "小张"},
     {id: 2, name: "小李"},
     {id: 3, name: "小孙"},
     {id: 1, name: "小周"},
     {id: 2, name: "小陈"},
];

let obj = {};

person = person.reduce((cur,next) => {
    obj[next.id] ? "" : obj[next.id] = true && cur.push(next);    return cur;
},[]) //设置cur默认类型为数组，并且初始值为空的数组
log(person);

After printing person, we can get the deduplicated array.

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