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();
   }

does [`indexOf`](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Array/indexOf) not work for you? — Nina Scholz, Jan 06 '17 at 10:56
no , but if I remove some array elements it will again cause error, so I am avoiding to use with indexOf — Prasad_Joshi, Jan 06 '17 at 10:57
see this:http://stackoverflow.com/questions/237104/how-do-i-check-if-an-array-includes-an-object-in-javascript — Suchit kumar, Jan 06 '17 at 10:59
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, Jan 06 '17 at 11:03

score 1 · Answer 1 · answered Feb 08 '17 at 17:30

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

score 0 · Answer 2 · answered Jan 06 '17 at 11:05

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>

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? — Prasad_Joshi, Jan 06 '17 at 11:08

score 0 · Answer 3 · answered Jan 06 '17 at 12:56

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');
}

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

3 Answers3