How to toggle a boolean?

bool = !bool;

This holds true in most languages.

If you don't mind the boolean being converted to a number (that is either 0 or 1), you can use the Bitwise XOR Assignment Operator. Like so:

bool ^= true;   //- toggle value.

let inDynamicEditMode   = true;     // Value is: true (boolean)
inDynamicEditMode      ^= true;     // Value is: 0 (number)
inDynamicEditMode      ^= true;     // Value is: 1 (number)
inDynamicEditMode      ^= true;     // Value is: 0 (number)

This is easier for me to scan than repeating the variable in each line.

This method works in all (major) browsers (and most programming languages).

bool = bool != true;

One of the cases.

Let's see this in action:

var b = true; console.log(b); // true b = !b; console.log(b); // false b = !b; console.log(b); // true

Anyways, there is no shorter way than what you currently have.

I was searching after a toggling method that does the same, but which "toggles" an initial value of null or undefined to false.

Here it is:

booly = !(booly != false)

bool === tool ? bool : tool

if you want the value to hold true if tool (another boolean) has the same value

In a case where you may be storing true / false as strings, such as in localStorage where the protocol flipped to multi object storage in 2009 & then flipped back to string only in 2011 - you can use JSON.parse to interpret to boolean on the fly:

this.sidebar = !JSON.parse(this.sidebar);

I always liked Boolean value, but nowadays I'm using binary for both convenience and debugging. You can use de consept !key : ++key: --key to toggle, and if you are in any asynchronous function or anytime an error or false true occurs, the value will leak out of 0(zero)/ 1(one) and you can trigger an alert to debug later.