how to check if a value in array is already exists & if not push it in array

Question

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. here is my code snippet.

<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();
   }

no , but if I remove some array elements it will again cause error, so I am avoiding to use with indexOf — Prasad_Joshi
– Prasad_Joshi, Commented Jan 6, 2017 at 10:57
you have also a security problem with localStorage and a syntax error here ` } else if ((newItem.value) === fruits[i].value)) {` to much parenthesis. — Nina Scholz
– Nina Scholz, Commented Jan 6, 2017 at 11:03

user2962151 · Accepted Answer · 2017-02-08 17:30:26Z

1

Simple use this check:

!!~array.indexOf(element)

It returns true if element is in array, returns false if element is absent.

You can also extend Array type with your own method (i.e. contains), to use it in your code, like this:

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

answered Feb 8, 2017 at 17:30

user2962151

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Comments

Gaurav joshi · Accepted Answer · 2017-01-06 11:05:02Z

0

Please add your local storage code and fillStcok function for complete functionality. The following snippet is for checking duplicate

    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>

answered Jan 6, 2017 at 11:05

Gaurav joshi

1,7971 gold badge15 silver badges28 bronze badges

1 Comment

Prasad_Joshi Over a year ago

thanks for answer, but what if some array elements are again removed, I saw errors when array elements are removed if we use indexOf in if else condition. How we can achieve it while keeping array intact?

Leonid Lazaryev · Accepted Answer · 2017-01-06 12:56:23Z

0

You can always use Array.prototype.find() method, with small extend. It's fast and synchronious. 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');
}

answered Jan 6, 2017 at 12:56

Leonid Lazaryev

3261 silver badge8 bronze badges

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