How to check all values of an array are equal or not in JavaScript ?

Given a javaScript array and the task is to print true if all the values of array are same using javaScript.

Approach 1:

  • First get the array of elements.
  • Pass it to an arrow function, which calls every() method on each array element and return true if each element matches with the first element of the array.

Example 1: This example uses array.every() method to print the desired response.

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<!DOCTYPE HTML> 
<html
    <head
        <title
            Check if all values of array are
            equal using JavaScript functions
        </title>
    </head
      
    <body style = "text-align:center;"
          
        <h1 style = "color:green;"
            GeeksForGeeks 
        </h1>
          
        <p id = "GFG_UP" style =
            "font-size: 15px; font-weight: bold;">
        </p>
          
        <button onclick = "gfg_Run();">
            click here
        </button>
          
        <pre id = "GFG_DOWN" style =
            "color:green; font-size: 20px; font-weight: bold;">
        </pre>
          
        <script>
            var el_up = document.getElementById("GFG_UP");
            var el_down = document.getElementById("GFG_DOWN");
              
            var arr = [1, 1, 1, 1];
              
            el_up.innerHTML = 
            "Click on button to check if all values are"
                    + " equal<br><br>" + arr;
              
            const allEqual = 
                    arr => arr.every( v => v === arr[0] );
              
            function gfg_Run() {
                el_down.innerHTML = allEqual(arr);
            }         
        </script
    </body
</html>

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Output:

  • Before clicking on the button:
  • After clicking on the button:

Approach 2:

  • First get the array of elements.
  • Pass it to a function, which calls reduce() method on array element.
  • Return true if each element matches with the first element of the array.

Example: This example uses array.reduce() method to print the false for the given array.

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<!DOCTYPE HTML> 
<html
    <head
        <title
            Check if all values of array are 
            equal using JavaScript functions
        </title>
    </head
      
    <body style = "text-align:center;">
           
        <h1 style = "color:green;"
            GeeksForGeeks 
        </h1>
          
        <p id = "GFG_UP" style
            "font-size: 15px; font-weight: bold;">
        </p>
          
        <button onclick = "gfg_Run();">
            click here
        </button>
          
        <pre id = "GFG_DOWN" style =
            "color:green; font-size: 20px; font-weight: bold;">
        </pre>
          
        <script>
            var el_up = document.getElementById("GFG_UP");
            var el_down = document.getElementById("GFG_DOWN");
          
            var arr = ["GFG", "GFG", "GFG", "GfG"];
          
            el_up.innerHTML = "Click on button to check if all"
                    + " values are equal<br><br>" + arr;
          
            function allEqual(arr) {
                if(!arr.length) return true;
                return arr.reduce(function(a, b)
                    {return (a === b)?a:(!b);}) === arr[0];
            }        
              
            function gfg_Run() {
                el_down.innerHTML = allEqual(arr);
            }         
        </script
    </body
</html>                    

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Output:

  • Before clicking on the button:
  • After clicking on the button:


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