对象值循环答案

【问题标题】：Object value loop对象值循环
【发布时间】：2020-06-05 23:06:22
【问题描述】：

我正在尝试使用 if 语句进行循环，其中 if 语句应该跳过空值。但有些如何它不会识别空值。

我的数组对象值有这个

[ { "id": 17, "match_id": 17, "dktournament_id": 10, "seed_match": 1, "created_at": "2020-02-11 21:37:47", "updated_at": "2020-02-11 21:37:53", "score": { "id": 17, "playerOne": "Knud", "playerTwo": "Weise", "setOne": 3, "setTwo": 0, "created_at": "2020-02-11 21:37:53", "updated_at": "2020-02-11 21:38:21" } }, { "id": 18, "match_id": 18, "dktournament_id": 10, "seed_match": 2, "created_at": "2020-02-11 21:37:47", "updated_at": "2020-02-11 21:39:07", "score": { "id": 18, "playerOne": "Hans", "playerTwo": "Khan", "setOne": 0, "setTwo": 3, "created_at": "2020-02-11 21:39:07", "updated_at": "2020-02-11 21:39:42" } }, { "id": 19, "match_id": 19, "dktournament_id": 10, "seed_match": 3, "created_at": "2020-02-11 21:37:47", "updated_at": "2020-02-11 21:44:12", "score": { "id": 19, "playerOne": "Preben", "playerTwo": "Gertrud", "setOne": 1, "setTwo": 0, "created_at": "2020-02-11 21:44:12", "updated_at": "2020-02-21 12:24:39" } }, { "id": 20, "match_id": 20, "dktournament_id": 10, "seed_match": 4, "created_at": "2020-02-11 21:37:47", "updated_at": "2020-02-11 21:58:02", "score": { "id": 20, "playerOne": "Ingvard", "playerTwo": "Oscar", "setOne": 0, "setTwo": 0, "created_at": "2020-02-11 21:58:02", "updated_at": "2020-02-11 21:58:02" } }, { "id": 21, "match_id": null, "dktournament_id": 10, "seed_match": 5, "created_at": "2020-02-11 21:37:47", "updated_at": "2020-02-11 21:37:47", "score": null }, { "id": 22, "match_id": null, "dktournament_id": 10, "seed_match": 6, "created_at": "2020-02-11 21:37:47", "updated_at": "2020-02-11 21:37:47", "score": null }, { "id": 23, "match_id": null, "dktournament_id": 10, "seed_match": 7, "created_at": "2020-02-11 21:37:47", "updated_at": "2020-02-11 21:37:47", "score": null }, { "id": 24, "match_id": null, "dktournament_id": 10, "seed_match": 8, "created_at": "2020-02-11 21:37:47", "updated_at": "2020-02-11 21:37:47", "score": null } ]

我的方法是这样的

totalsetsTeamOne(){
                let i;
                let SetOneTotal = 0;
                for (i = 0; i < 8; i++) {
                    if(this.seedmatches[i]!= null){
                        SetOneTotal += this.seedmatches[i].score.setOne;
                    }
                }
                this.setOneTotal = SetOneTotal;
                console.log(SetOneTotal)
            },

我的错误是这样的

[Vue warn]: Error in mounted hook: "TypeError: Cannot read property 'setOne' of null"

【问题讨论】：

错误表示this.seedmatches[i].score是null。
this.seedmatches[i] 不是空值，它是其中之一上的score 对象。
它就在您发布的数组中：最后几个条目有"score": null。
@JeremyHarris 我想在 seedmatches[i] 为 NULL 时跳过该值。 Butt 不知何故它不会跳过它，这就是为什么我得到 setOne 的错误，因为它是 null
@SajidLatif 您没有阅读 cmets 或答案吗？问题是某些对象的 score 属性是null。 查看您自己在问题中发布的数组。

标签： javascript arrays vue.js object

【解决方案1】：

这里有两个版本的计算，使用表达式。

第二个使用optional chaining operator。

const data = [ { "id": 17, "match_id": 17, "dktournament_id": 10, "seed_match": 1, "created_at": "2020-02-11 21:37:47", "updated_at": "2020-02-11 21:37:53", "score": { "id": 17, "playerOne": "Knud", "playerTwo": "Weise", "setOne": 3, "setTwo": 0, "created_at": "2020-02-11 21:37:53", "updated_at": "2020-02-11 21:38:21" } }, { "id": 18, "match_id": 18, "dktournament_id": 10, "seed_match": 2, "created_at": "2020-02-11 21:37:47", "updated_at": "2020-02-11 21:39:07", "score": { "id": 18, "playerOne": "Hans", "playerTwo": "Khan", "setOne": 0, "setTwo": 3, "created_at": "2020-02-11 21:39:07", "updated_at": "2020-02-11 21:39:42" } }, { "id": 19, "match_id": 19, "dktournament_id": 10, "seed_match": 3, "created_at": "2020-02-11 21:37:47", "updated_at": "2020-02-11 21:44:12", "score": { "id": 19, "playerOne": "Preben", "playerTwo": "Gertrud", "setOne": 1, "setTwo": 0, "created_at": "2020-02-11 21:44:12", "updated_at": "2020-02-21 12:24:39" } }, { "id": 20, "match_id": 20, "dktournament_id": 10, "seed_match": 4, "created_at": "2020-02-11 21:37:47", "updated_at": "2020-02-11 21:58:02", "score": { "id": 20, "playerOne": "Ingvard", "playerTwo": "Oscar", "setOne": 0, "setTwo": 0, "created_at": "2020-02-11 21:58:02", "updated_at": "2020-02-11 21:58:02" } }, { "id": 21, "match_id": null, "dktournament_id": 10, "seed_match": 5, "created_at": "2020-02-11 21:37:47", "updated_at": "2020-02-11 21:37:47", "score": null }, { "id": 22, "match_id": null, "dktournament_id": 10, "seed_match": 6, "created_at": "2020-02-11 21:37:47", "updated_at": "2020-02-11 21:37:47", "score": null }, { "id": 23, "match_id": null, "dktournament_id": 10, "seed_match": 7, "created_at": "2020-02-11 21:37:47", "updated_at": "2020-02-11 21:37:47", "score": null }, { "id": 24, "match_id": null, "dktournament_id": 10, "seed_match": 8, "created_at": "2020-02-11 21:37:47", "updated_at": "2020-02-11 21:37:47", "score": null } ]

const setOneTotal1 = (arr) => 
    arr.reduce((total, { score }) =>
        ((score && (total += score.setOne)), total), 0)
console.log(setOneTotal1(data))

const setOneTotal2 = (arr) => 
    arr.reduce((total, {score}, _, __, s1 = score?.setOne) => 
        (s1 ? total + s1 : total), 0)
console.log(setOneTotal2(data))

【讨论】：

【解决方案2】：

此代码将起作用..试试这个...

totalsetsTeamOne() {
    let i;
    let SetOneTotal = 0;
    for (i = 0; i < 8; i++) {
        if (this.seedmatches[i] && this.seedmatches[i].score !== null) {
            SetOneTotal += seedmatches[i].score.setOne;
        }
    }
    this.setOneTotal = SetOneTotal;
    console.log(SetOneTotal)
},

【讨论】：

【解决方案3】：

你的 if 语句应该是

 if(this.seedmatches[i] && this.seedmatches[i].score){
      SetOneTotal += this.seedmatches[i].score.setOne;
 }

因为您只检查 this.seedmatches[i] 中是否有值。但是如果 this.seedmatches[i] 中有值但 this.seedmatches[i].score 为空怎么办？因此，我们需要彻底检查 this.seedmatches[i].score 是否也为空。

【讨论】：

【解决方案4】：

您正在查看 this.seedmatches[i] 是否为空，而不是 this.seedmatches[i].score 是否为空

【讨论】：

【解决方案5】：

因为 "id": 21 和其他项目有 "score":null

【讨论】：

我知道。这就是为什么我想跳过它