Question

在Js中工作时，我需要检查数组中的值是否存在＆amp;如果它存在对用户显示错误，＆amp;如果没有把它推入阵列。这是我的代码片段。

<html>
<body>
<label>Enter an New item to add in Stock</label>
<br> </br>
<input type="text" name=" itemName" id="addItemInStock">
<br></br>
<p id="errorMsg"></p>
<button onclick="addToStock()">Add</button>
<p id="showList"></p>
<select id="showInDropDown">
    <option disabled selected style="display: block;">Stock Items</option>
</select>
<script>
    var fruitsfromLS = localStorage.getItem("fruits");
    var fruits = fruitsfromLS ? JSON.parse(fruitsfromLS) : ["Banana", "Orange", "Apple", "Mango"];
    //document.getElementById("showList").innerHTML = fruits;
    var newItem = document.getElementById("addItemInStock");

    function addToStock() {
        if ((newItem.value) === "") {
            document.getElementById("errorMsg").innerHTML = "Blank item cannot be added!!";
            document.getElementById("errorMsg").style.display = "block";
        } else if ((newItem.value) === fruits[i].value)) {
        document.getElementById("errorMsg").innerHTML = "aLREADY IN sTOCK!";
        document.getElementById("errorMsg").style.display = "block";
    } else {
        document.getElementById("errorMsg").style.display = "none";
        fruits.push(newItem.value);
        localStorage.setItem("fruits", JSON.stringify(fruits));
        clearAndShow();
    }
    fillSelect();
   }

Answer 1

简单使用此检查：

!!~array.indexOf(element)

如果element在数组中，则返回true;如果element不存在，则返回false。

您还可以使用自己的方法（即包含）扩展Array类型，以便在代码中使用它，如下所示：

Array.prototype.contains = Array.prototype.contains || function(element) {
    return !!~this.indexOf(element);
};

let a = [ -2, -1, 0, 1, 2, 3, 4, 5 ]; // an example of array

console.log( a.contains(-1) );  // true
console.log( a.contains(10) );  // false

Answer 2

请添加本地存储代码和fillStcok功能以获得完整功能。以下代码段用于检查重复的

    var fruits = ["Banana", "Orange", "Apple", "Mango"];
    //document.getElementById("showList").innerHTML = fruits;
    var newItem = document.getElementById("addItemInStock");

    function addToStock() {
        if (newItem.value === "") {
            document.getElementById("errorMsg").innerHTML = "Blank item cannot be added!!";
            document.getElementById("errorMsg").style.display = "block";
        } else if (fruits.indexOf(newItem.value) !== -1) {
          document.getElementById("errorMsg").innerHTML = "ALREADY IN STOCK!";
          document.getElementById("errorMsg").style.display = "block";
        } else {
          document.getElementById("errorMsg").style.display = "none";
          fruits.push(newItem.value);
      }
   }

<label>Enter an New item to add in Stock</label>
<br> </br>
<input type="text" name=" itemName" id="addItemInStock">
<br></br>
<p id="errorMsg"></p>
<button onclick="addToStock()">Add</button>
<p id="showList"></p>
<select id="showInDropDown">
    <option disabled selected style="display: block;">Stock Items</option>
</select>

Answer 3

您可以始终使用Array.prototype.find（）方法，只需小扩展。它快速而同步。 https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Array/find

var findFunc = function(searchVal, element, index, arr) {
  return searchVal == element
}

var freshOne = fruits.find(findFunc.bind(undefined, newItem.value)) == undefined;

if (freshOne) {
    fruits.push(newItem.value)
} else {
    console.log('Already there');
}

如何检查数组中的值是否已存在＆amp;如果没有把它推入阵列

3 个答案: