如何在 Javascript 的 MAP 中检查 VALUE 是否存在？

How can I check if an VALUE exists in MAP on Javascript?

提问by Fernando Maymone

It looks a very easy question but i didnt find it in any place.

这看起来是一个非常简单的问题，但我没有在任何地方找到它。

How can I know If an value exists in a Map?

我如何知道 Map 中是否存在某个值？

For example:

例如：

A = [1,2,3,5,6,7]
var myMap = new Map();
    for (let i = 0; i < A.length; i++) {
        myMap.set(i,A[i]);
    }
    for (let z = 1; z < Number.MAX_SAFE_INTEGER; z++) {
        console.log(z);
        if(!myMap.hasValue(z)){
            return z;
        }
    }

I want to check if, given one value, this VALUE is on the Hash. Like a "hasValue"

我想检查给定一个值，这个 VALUE 是否在哈希上。就像一个“hasValue”

采纳答案by Dario

You can use iterate over the map, look for the value and return true (exiting the loop) as soon as you find it. Or you return false if the element does not exist. Something like:

您可以在地图上使用迭代，查找值并在找到后立即返回 true（退出循环）。或者，如果元素不存在，则返回 false。就像是：

const findInMap = (map, val) => {
  for (let [k, v] of map) {
    if (v === val) { 
      return true; 
    }
  }  
  return false;
}

回答by Bergi

You cannot, other than by searching through it:

除了通过搜索之外，您不能：

Array.from(myMap.values()).includes(val)

Use an appropriate data structure instead, like a set of all the values:

改用适当的数据结构，例如所有值的集合：

A = [1,2,3,5,6,7]
var myValues = new Set(A);

for (let z = 1; z < Number.MAX_SAFE_INTEGER; z++) {
    console.log(z);
    if(!myValues.has(z)) {
        return z;
    }
}

Of course, given the fact that your Ais sorted already, you could iterate it directly to find the lowest missing value.

当然，鉴于您A已经排序，您可以直接迭代它以找到最低的缺失值。

回答by Johannes Nielsen

I know this question is already answered, but I would like to point out a way to do this without (explicitly) iterating of the entries. You can do

我知道这个问题已经得到回答，但我想指出一种无需（显式）迭代条目的方法。你可以做

let myMap = new Map([[0, 1], [1, 2], [2, 3], [3, 5], [4, 6], [5, 7]])

for (let z = 1; z < Number.MAX_SAFE_INTEGER; ++z) {
    console.log(z);
    if([...myMap.values()].includes(z) === false){
        return z;
    }
}

So, you could create a function

所以，你可以创建一个函数

const mapContainsElement = (map, val) => [...map.values()].includes(v)

回答by Alan Yong

I, personally prefers to find, indexOfand findIndex.

我个人更喜欢find,indexOf和findIndex。

const array1 = (map, val) => {
  var foo;
  array2.find( (x) => foo = x === foo.id )
  return foo;
}

findIndex

查找索引

find

寻找

indexOf

指数

回答by Fohlen

Use Map.has(z), as described on MDN

使用Map.has(z)，如MDN 上所述