Check if String is Empty

To check if given string is empty in JavaScript, compare the given string with an empty string using Equal-to comparison operator.

The boolean expression that compares the string str and an empty string is

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str == ''

If the value is str is an empty string, the above expression returns true, or else, the expression returns false. We can use this expression in an if-else statement as follows.

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if (str == '') {
  //str is empty string
} else {
  //str is not empty string
}

Examples

In the following example, we take an empty string in str, programmatically check if str is empty string or not, and display the output in pre#output.

index.html

<!DOCTYPE html>
<html lang="en">
  <body>
    <pre id="output">Output : </pre>
    <script>
      var str = '';
      if ( str == '' ) {
        document.getElementById('output').innerHTML = 'str is empty';
      } else {
        document.getElementById('output').innerHTML = 'str is not empty';
      }
    </script>
  </body>
</html>

Since, the value in str is an empty string, if-block executes.

In the following example, we take a non-empty string value in str, say 'apple', programmatically check if str is empty string or not, and display the output in pre#output.

index.html

<!DOCTYPE html>
<html lang="en">
  <body>
    <pre id="output">Output : </pre>
    <script>
      var str = 'apple';
      if ( str == '' ) {
        document.getElementById('output').innerHTML = 'str is empty';
      } else {
        document.getElementById('output').innerHTML = 'str is not empty';
      }
    </script>
  </body>
</html>

Since, the value in str is not an empty string, else-block executes.

Conclusion

In this JavaScript Tutorial, we learned how to check if given string is empty or not using Equal-to comparison operator, with example program.