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

Last Updated : 19 Jun, 2019

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.

<!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>

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.

<!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>                    

Output:

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

My Personal Notes

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