Double negation coerces any value in JS to a Boolean of true or false.
It is important to know that there are seven values that evaluate as false in an evaluation context, these "falsy" values are as follows:
1. false
2. 0
3. -0
4. NaN
5. null
6. undefined
7. "" // empty string
Every other value is truthy.
Knowing this can clean up and cut down a lot of code. Personally it irks me to no end when I see something like...
if (v === null || v === undefined ...) return null;
Which can be more easily evaluated as `(!v)` first... sometimes you'll want to allow 0 `(!v && v !== 0)`
Double negation coerces any value in JS to a Boolean of true or false. It is important to know that there are seven values that evaluate as false in an evaluation context, these "falsy" values are as follows: 1. false 2. 0 3. -0 4. NaN 5. null 6. undefined 7. "" // empty string Every other value is truthy. Knowing this can clean up and cut down a lot of code. Personally it irks me to no end when I see something like... if (v === null || v === undefined ...) return null; Which can be more easily evaluated as `(!v)` first... sometimes you'll want to allow 0 `(!v && v !== 0)`