JavaScript every(): Check if All Values in an Array are True

The JavaScript every() method is used when we need to execute a function for each and every element of a specified array that returns true if all elements meet the specified condition that is defined inside the function; otherwise, it returns false. For example:

HTML with JavaScript Code

<!DOCTYPE html>
<html>
<body>

   <p id="xyz"></p>
   
   <script>
      const myNumbers = [12, 32, 48, 54, 66];
      let x = myNumbers.every(checkEven);

      function checkEven(num)
      {
         return num%2==0;
      }
      
      if(x==true)
      {
         document.getElementById("xyz").innerHTML = "All are even numbers";
      }
      else
      {
         document.getElementById("xyz").innerHTML = "All are not even numbers";
      }
   </script>
   
</body>
</html>

Output

If num%2==0 returns false for any element, then the function every() returns false as a whole. For example:

HTML with JavaScript Code

<!DOCTYPE html>
<html>
<body>

   <p id="abc"></p>
   
   <script>
      const myNumbers = [13, 32, 48, 54, 66];

      function checkEven(num) {
         return num%2==0;
      }
      
      if(myNumbers.every(checkEven))
         document.getElementById("abc").innerHTML = "All are even numbers";
      else
         document.getElementById("abc").innerHTML = "All are not even numbers";
   </script>
   
</body>
</html>

Output

JavaScript every() syntax

The syntax of the every() method in JavaScript is:

array.every(functionName(currentElementValue, currentElementIndex, currentElementArray), thisValue)

The array, functionName, and currentElementValue are required. Whereas all others are optional.

Note: The array refers to an array whose each and every element wants to check for the particular condition using a specified functionName.

Note: The functionName refers to a function to be executed for every element of the array.

Note: The currentElementValue basically refers to a variable that will be used as an argument to the function and that, of course, indicates the current value or element of the specified array.

Note: The currentElementIndex refers to the index of the current element.

Note: The currentElementArray refers to the array of the current element.

Note: The thisValue refers to a value passed to the specified function, functionName as its this value.

JavaScript every() example

Consider the following code as an example demonstrating the every() method in JavaScript:

HTML with JavaScript Code

<!DOCTYPE html>
<html>
<body>

   <p>Leaving first and last element<br>
      <span id="res"></span>
   </p>
   
   <script>
      const nums = [13, 32, 48, 54, 66, 89];

      function even(val, indx, arr) {
         if(indx==0)
            return true;
         if(indx == arr.length-1)
            return true;
         return val%2==0;
      }
      
      if(nums.every(even))
         document.getElementById("res").innerHTML = "All are even numbers";
      else
         document.getElementById("res").innerHTML = "All are not even numbers";
   </script>
   
</body>
</html>

Output

Leaving first and last element

Since indexing always starts with 0, therefore, subtracting 1 from the length of an array refers to the index of the last element.

JavaScript Online Test

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