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Calculate the length of an associative array using JavaScript

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  • Last Updated : 12 Dec, 2021
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Associative Array: In JavaScript, we have normal arrays in which an element is present at a particular index. Whereas Associative arrays are basically Objects in JavaScript where the index is replaced with user-defined keys. Basically, we can say that it stores Key-Value pairs.

Syntax:

let arr = { key1: 'value'1, key2: 'value2', key3: 'value3'}

Here, arr is the associative array, and key1, key2, and key3 are its indexes, and value1, value2, and value3 are its elements.

Example:

let arr = {"apple": 10, "grapes": 20};

Javascript




<script>
    let arr = {
        "apple": 10,
        "grapes": 20
    };
    arr["guava"] = 30;
    arr["banana"] = 40;
    document.writeln("Apple = " + arr.apple)
    document.write("Banana = " + arr.banana)
</script>

  Output:

Apple = 10 Banana = 40

Length of an associative array: Like in a normal array, an associative array does not have a length property. So we will see other ways to calculate the length of associative arrays.

To calculate the length of an associative array, we will traverse the array element and count all the keys present in the array.

Javascript




<script>
 
    // Function to calculate the
    // length of an array
    sizeOfArray = function (array) {
 
        // A variable to store
        // the size of arrays
        let size = 0;
 
        // Traversing the array
        for (let key in array) {
 
            // Checking if key is present
            // in arrays or not
            if (array.hasOwnProperty(key)) {
                size++;
            }
        }
 
        // Return the size
        return size;
    }
 
    // Driver code
    let arr = { "apple": 10, "grapes": 20 };
    arr["guava"] = 30;
    arr["banana"] = 40;
 
    // Printing the array
    console.log(arr);
 
    // Printing the size
    console.log("size = " + sizeOfArray(arr));
 
    // Adding another element to array
    arr["fruits"] = 100;
 
    // Printing the array and size again
    console.log(arr);
    console.log("Size = " + sizeOfArray(arr));
</script>

Output:

{apple: 10, grapes: 20, guava: 30, banana: 40}
size = 4
{apple: 10, grapes: 20, guava: 30, banana: 40, fruits: 100}
Size = 5

Using  the keys method: The keys() method returns an array containing all the keys present in the associative array. So, we can use the length property on this array to get the length of associative array.

Javascript




<script>
    let arr = { "apple": 10, "grapes": 20 };
    arr["guava"] = 30;
    arr["banana"] = 40;
 
    // Printing the array
    // returned by keys() method
    console.log(Object.keys(arr))
 
    // printing the size
    console.log("Size = " + Object.keys(arr).length)
</script>

Output:

['apple', 'grapes', 'guava', 'banana']
Size = 4

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