How to toggle a boolean?

bool = !bool;

This holds true in most languages.

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.

bool = bool != true;

One of the cases.

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).