From my understanding, I believe that var a = 1; is the only truthy and the rest are falsy’s - is this correct?

No.

1. 
   

   var a = 0;

   
   

   
   
   

   Number zero is falsy. However, note that the string zero 0 is truthy.




2. 
   

   var a = 10 == 5;

   
   

   
   
   

   This is same as var a = (10 == 5);, so this is falsy.




3. 
   

   var a = 1;

   
   
   

   var a = -1;

   
   

   
   
   

   Any non-zero number including negative numbers is truthy.

Quoting from MDN

In JavaScript, a truthy value is a value that translates to true when evaluated in a Boolean context. All values are truthy unless they are defined as falsy (i.e., except for false, 0, , null, undefined, and NaN).

List of falsy values in JavaScript:^{From MDN}

1. false


2. null


3. undefined


4. 0


5. NaN


6. '', , ``(Empty template string)


7. document.all


8. 0n: BigInt


9. -0