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Difference between array.size() and array.length in JavaScript

  • Difficulty Level : Expert
  • Last Updated : 16 Apr, 2020

The array.size() method is functionally equivalent to the array.length property and it can be only used in jQuery. Here in JavaScript array.size() is invalid method so array.length property should be used.

Below examples implement the above concept:

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Example 1: This example demonstrates array.size() method and array.length property.




<!DOCTYPE html>
<html>
  
<head>
    <title>
        Difference between array.size() method
        and array.length property
    </title>
</head>
  
<body>
    <p>
        Click the button to display
        the length of array.
    </p>
  
    <button onclick="findLength()">
        Try it
    </button>
  
    <p>
        Length of the array is: 
        <span id="demo"></span>
    </p>
  
    <script>
        var arr = ['geeks', 'for', 'geeks'];
  
        function findLength() {
            document.getElementById("demo").innerHTML
                        = arr.length;
              
            document.getElementById("demo").innerHTML
                        = arr.size();
        }
    </script>
</body>
  
</html>

Output:



Length of the array is: 3
error on console: TypeError: arr.size is not a function

Note: The array.length property returns value of last_key+1 for Arrays with numeric index value. This property doesn’t guarantee to find the number of items in the array.

Example 2: This example display how Array.length property works.




<!DOCTYPE html>
<html>
  
<head>
    <title>
        Array.length property
    </title>
</head>
  
<body>
    <p>
        Click the button to display
        the length of array.
    </p>
  
    <button onclick="findLength()">
        Try it
    </button>
  
    <p>
        Length of array the is: 
        <span id="demo"></span>
    </p>
  
    <script>
        var arr = ['geeks', 'for', 'geeks'];
        arr[50] = 'article';
          
        function findLength() {
            document.getElementById("demo")
                        .innerHTML = arr.length;
        }
    </script
</body>
  
</html>

Output:

Length of the array is: 51

Example 3: This example display how array.length property works when index key is non numeric.




<!DOCTYPE html>
<html>
  
<head>
    <title>
        array.length property with
        non-numeric index key
    </title>
</head>
  
<body>
    <p>
        Click the button to display
        the length of array.
    </p>
  
    <button onclick="findLength()">
        Try it
    </button>
  
    <p>
        Length of array the is: 
        <span id="demo"></span>
    </p>
  
    <script>
        var arr = new Array();
        arr['a'] = 1;
        arr['b'] = 2;
        arr['c'] = 3;
          
        function findLength() {
            document.getElementById("demo")
                    .innerHTML = arr.length;
        }
    </script
</body>
  
</html>

Output:

Length of the array is: 0



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