如何检查数组中的值是否已经存在以及是否不将其推送到数组中
[英]how to check if a value in array is already exists & if not push it in array
问题描述
while working around in Js, I need to check if a value in array is present or not & if it exists show error to user, & if not push it in array. 
在Js中解决时，我需要检查数组中的值是否存在以及是否存在向用户显示错误，以及是否不将其推送到数组中。 here is my code snippet. 这是我的代码段。
<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();
}
3 个解决方案
解决方案1
1 2017-02-08 17:30:26
Simple use this check: 简单使用此检查：
!!~array.indexOf(element)
It returns true if element is in array, returns false if element is absent. 如果element在数组中，则返回true；如果没有element，则返回false。
You can also extend Array type with your own method (ie contains), to use it in your code, like this: 您还可以使用自己的方法（即包含）扩展Array类型，以在代码中使用它，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
解决方案2
0 2017-01-06 11:05:02
Please add your local storage code and fillStcok function for complete functionality.
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>
解决方案3
0 2017-01-06 12:56:23
You can always use Array.prototype.find() method, with small extend. 您始终可以使用Array.prototype.find（）方法，并进行少量扩展。 It's fast and synchronious. 快速而同步。 https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Array/find https://developer.mozilla.org/zh-CN/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');
}
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