Undefined: The Third Boolean Value

This article explores a clever approach to implementing a notification system mirroring Google Docs' save indicator, using a boolean variable to represent three states: "Saving...", "Saved", and an initial "nothing" state.

The initial instinct is to use a boolean isSaving variable, rendering "Saving..." when true and "All changes saved" when false. However, this leaves a UX problem: on initial page load, "All changes saved" displays, which is inaccurate.

The solution leverages JavaScript's undefined state. When isSaving is first declared (let isSaving;), its value is undefined. This provides the third state needed.

The challenge lies in differentiating between undefined and false in the conditional rendering. A simple ternary operator won't suffice because both undefined and false evaluate to falsy in a standard ternary expression.

The solution employs a nested ternary operator for precise control:

{{ isSaving === true ? 'Saving...' : (isSaving === false ? 'All changes saved' : '') }}

This explicitly checks for true and false, rendering an empty string when isSaving is undefined.

Alternatively, if the templating engine supports if/else statements, a cleaner solution is possible:

{% if isSaving === true %}
  Saving...
{% elseif isSaving === false %}
  All changes saved
{% endif %}

This approach elegantly handles the three states, displaying nothing until a save operation begins. This method cleverly utilizes the undefined state inherent in JavaScript variable declaration to achieve a desired three-state behavior without resorting to a string variable or other more complex solutions.

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