if statements only allow SINGLE boolean expressions

[coolaj86]

This rule is taken from Zig.

❌ Bad Example

if (!(new Date() < expiresAt && new Date() > activeAt)) {
    throw new Error("not valid");
}

if (!(Date.now() < expires)) {
    throw new Error("expired");
}

✅ Good Example

let now = Date.now();
let isValid = now < expiresAt && now >= activeAt;
if (!isValid) {
    throw new Error("not valid");
}

let now = Date.now();
let isActive = now < expiresAt;
if (!isActive) {
    throw new Error("expired");
}

Rationale

Complex expressions become quadratically more difficult as they are expanded. Limiting if statements to simple expressions improves readability, generally, and also causes the code to become more self-documenting (i.e. isActive vs now < expiresAt && now >= activeAt).

Also, due to the nature of JavaScript (i.e. NaN comparisons), it's easy to have false conditions such as now > expires_at == false when bugs have crept in now > NaN == false.

Using named boolean expressions (i.e. isActive) that can easily be negated (i.e. !isActive) improves correctness and security.