如何在 Javascript 中更改 Array 对象的值

Question

我有一个数组对象调用 listOfObjects。

[{"name":"A", "data":"[{"value1":"1","value2":"2"}]"},
 {"name":"B", "data":"[{"value1":"1","value2":"2"}]"}]

我想要做的是将一个对象插入到数组为空的数组中。如果数组不为空，则检查里面的项目。如果项目已经存在，请更新项目，否则将其添加到数组中。下面是我的代码

  var searchName= "A"; 
  if (listOfObjects.length > 0) {
            for (var i = 0; i < listOfObjects.length; i++) {
                if (listOfObjects[i].name == searchName) {
                    listOfObjects[i].data = data;
                    break;
                } else {
                    insert = {
                        'name': searchName,
                        'data': data
                    };
                    listOfObjects.push(insert);
                }
            }
    } else {
        insert = {
            'name': searchName,
            'data': data
        };
        listOfObjects.push(insert);
   }

当我运行它时，即使 A 已经存在，它也会更新现有项目，但还会在 listOfObjects 中再添加一次。反正有没有可以实现我想要的？谢谢..

Answer 1

问题是您要插入数组inside for 循环以寻找匹配项。相反，请记住您是否看过匹配项，如果没有，请在循环之后插入。 length 检查也没有理由，也没有理由重复插入的逻辑：

var searchName= "A"; 
var found = false;
for (var i = 0; !found && i < listOfObjects.length; i++) {
    if (listOfObjects[i].name == searchName) {
        listOfObjects[i].data = data;
        found = true;
    }
}
if (!found) {
    listOfObjects.push({
        'name': searchName,
        'data': data
    });
}

---

请注意，如果您愿意，可以使用Array#find（可以为旧浏览器填充）来查找条目，而不是使用for 循环：

var searchName= "A"; 
var entry = listOfObjects.find(function(entry) {
    return entry.name == searchName;
});
if (entry) {
    entry.data = data;
} else {
    listOfObjects.push({
        'name': searchName,
        'data': data
    });
}

Answer 2

首先改变这个

[{"name":"A", "data":"[{"value1":"1","value2":"2"}]"},
 {"name":"B", "data":"[{"value1":"1","value2":"2"}]"}]

由

[{"name":"A", "data":[{"value1":1,"value2":2}]},
 {"name":"B", "data":[{"value1":"1","value2":"2"}]}];

因为你的名单会throw Uncaught SyntaxError: Unexpected identifier

Answer 3

编写另一个简单的函数来获取带有选定搜索名称的项目 listOfObjects[i]。这里的“getSearchObject()”函数检查 searchName 的存在，然后添加或更新数组。

addOrRemoveItem() {
    let listOfObjects = [
      { "name": "A", "data": "[{'value1':'1','value2':'2'}]" },
      { "name": "B", "data": "[{'value1':'1','value2':'2'}]" }
    ],
      data = '[{"value1":"1","value2":"2"}]';
    var searchName = "C";
    if (listOfObjects.length > 0) {
      let searchObj = this.getSearchObject(listOfObjects, searchName);
      if (searchObj) {
        searchObj.data = data;
      } else {
        let insert = {
          "name": searchName,
          "data": data
        }
        listOfObjects.push(insert);
      }
    } else {
      let insert = {
        "name": searchName,
        "data": data
      }
      listOfObjects.push(insert);
    }
  }

  getSearchObject(objArr, searchKey) {
    var obj = null;
    for (let i = 0; i < objArr.length; i++) {
      if (objArr[i].name === searchKey) {
        obj = objArr[i];
      }
    }
    return obj;
  }

Answer 4

一个通用的解决方案，可以识别较旧的 JS 引擎（filter 而不是 find），但始终假设可以通过这样的方式实现唯一项目列表...

function updateList(itemList, item) { // - always assume a list of unique items.
  var
    itemName = item.name,
    listItem = itemList.filter(function (elm) { // - assume `filter`, not find`.
      return (elm.name === itemName); // - find/get existing list  item by name.
    })[0];

  if (listItem) {
    listItem.data = item.data;
  } else {
    itemList.push(item)
  }
}


var list = [
  { "name": "A", "data": [ { "value1": "A1", "value2": "A2" }] },
  { "name": "B", "data": [ { "value1": "B1", "value2": "B2" }] },
  { "name": "C", "data": [ { "value1": "C1", "value2": "C2" }] }
];

console.log('list : ', list);


updateList(list,  { "name": "D", "data": [ { "value1": "D1", "value2": "D2" }] });

updateList(list,  { "name": "B", "data": [ { "value1": "b_1", "value2": "b_2", "value3": "b_3" }] });
updateList(list,  { "name": "C", "data": [ { "value3": "C3" }] });

console.log('list : ', list);

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