Conditional Keydown JS

Follow these steps:

Identify the requirements: Determine the conditions that need to be met before allowing the keydown event to trigger the desired action.

Add an event listener: Attach a keydown event listener to the appropriate DOM element where you want to listen for the key press.

Check the requirements: Inside the event listener function, check if all the requirements are fulfilled. If they are, execute the desired action; otherwise, do nothing.

Let's say we want to trigger an alert when the user presses the Enter key (key code 13), but only if a text input field has some text in it.

HTML:

<input type="text" id="textInput" />

JavaScript:

// Step 1: Define the requirements
function areRequirementsFulfilled() {
  const textInputValue = document.getElementById('textInput').value;
  return textInputValue.trim() !== ''; // The requirement is that the input field should not be empty after trimming whitespace.
}

// Step 2: Add event listener
document.getElementById('textInput').addEventListener('keydown', function(event) {
  // Step 3: Check the requirements
  if (event.keyCode === 13 && areRequirementsFulfilled()) {
    // If the Enter key is pressed and all requirements are fulfilled, show an alert.
    alert('Requirements fulfilled! You can proceed.');
  } else {
    // If the Enter key is pressed but the requirements are not met, do nothing.
    event.preventDefault(); // Prevent the default Enter key behavior (e.g., form submission).
  }
});

Inside the keydown event listener, I check if the key pressed is the Enter key (key code 13) and if all the requirements are fulfilled. If so, I show an alert; otherwise, I prevent the default behavior (e.g., form submission) using event.preventDefault() and do nothing.