How many times a value exists in an array [duplicate]

Question

The first thing i am trying to do is find out if the number i type in the input exists in the array, this works.

The second thing I am trying to do is find out how many times it exists. Am I somewhat on the right path here?

<input id="hvorMange" type="number">
<button type="button" onclick="skrivUt12()">Finn tallet</button>
<p id="skrivUt12"></p> 



var liste = [12,14,13,76,5,1,23,12,87,124,674,98,3,7,-3,5];  


function skrivUt12(){

var tall = +document.getElementById("hvorMange").value;
var sum = 0;


for(i = 0; i < liste.length; i++) {
        if (tall === liste[i]) {
            sum++;
            document.getElementById("skrivUt12").innerHTML = "Tallet " + tall + " finnes " + sum + " antall ganger";
            return true;
        }
         else {
            document.getElementById("skrivUt12").innerHTML = "Tallet " + tall + " finnes ikke";
        }
    }
}

Answer 1

First you filter your list to keep searched items and then return the length of filtered list:

var liste = [12,14,13,76,5,1,23,12,87,124,674,98,3,7,-3,5];
var count = (input, arr) => arr.filter(x => x === input).length;
console.log (count(12, liste)); // 2

Answer 2

You may better use an object for counting and use it for checking and displaying the count.

var liste = [12, 14, 13, 76, 5, 1, 23, 12, 87, 124, 674, 98, 3, 7, -3, 5],
    count = {};

liste.forEach(function(a) {
    count[a] = (count[a] || 0) + 1;
});

console.log(count);

if (count[12]) {
    console.log('12 exist ' + count[12] + ' time/s');
} else {
    console.log('12 does not exist.');
}

.as-console-wrapper { max-height: 100% !important; top: 0; }