# JavaScript: Find duplicate values in a array

## JavaScript Array: Exercise-20 with Solution

Write a JavaScript program to find duplicate values in a JavaScript array.

Sample Solution:

JavaScript Code:

``````// Function to find duplicates in an array
function find_duplicate_in_array(arra1) {
// Object to store the count of each element in the array
var object = {};

// Array to store the elements with duplicates
var result = [];

// Iterate through each element in the array
arra1.forEach(function (item) {
// Check if the element is not in the object, initialize its count to 0
if (!object[item])
object[item] = 0;

// Increment the count of the current element
object[item] += 1;
})

// Iterate through the properties of the object
for (var prop in object) {
// Check if the count of the element is greater than or equal to 2
if (object[prop] >= 2) {
// Add the element to the result array
result.push(prop);
}
}

// Return the array containing duplicate elements
return result;
}

// Output the result of the function with a sample array
console.log(find_duplicate_in_array([1, 2, -2, 4, 5, 4, 7, 8, 7, 7, 71, 3, 6]));
```
```

Output:

```["4","7"]
```

Flowchart:

ES6 Version:

``````// Function to find duplicates in an array
const find_duplicate_in_array = (arra1) => {
// Object to store the count of each element in the array
const object = {};

// Array to store the elements with duplicates
const result = [];

// Iterate through each element in the array
arra1.forEach((item) => {
// Check if the element is not in the object, initialize its count to 0
if (!object[item]) {
object[item] = 0;
}

// Increment the count of the current element
object[item] += 1;
});

// Iterate through the properties of the object
for (const prop in object) {
// Check if the count of the element is greater than or equal to 2
if (object[prop] >= 2) {
// Add the element to the result array
result.push(prop);
}
}

// Return the array containing duplicate elements
return result;
};

// Output the result of the function with a sample array
console.log(find_duplicate_in_array([1, 2, -2, 4, 5, 4, 7, 8, 7, 7, 71, 3, 6]));
``````

Live Demo:

See the Pen JavaScript - Find duplicate values in a array - array-ex- 20 by w3resource (@w3resource) on CodePen.

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