Disallow negated conditions (no-negated-condition)

This rule disallows negated conditions in either of the following:

• if statements which have an else branch
• ternary expressions

Examples of incorrect code for this rule:

/*eslint no-negated-condition: "error"*/

if (!a) {
    doSomething();
} else {
    doSomethingElse();
}

if (a != b) {
    doSomething();
} else {
    doSomethingElse();
}

if (a !== b) {
    doSomething();
} else {
    doSomethingElse();
}

!a ? c : b

Examples of correct code for this rule:

/*eslint no-negated-condition: "error"*/

if (!a) {
    doSomething();
}

if (!a) {
    doSomething();
} else if (b) {
    doSomething();
}

if (a != b) {
    doSomething();
}

a ? b : c

http://eslint.org/docs/rules/no-negated-condition

[timoxley]

While I agree with this for the trivial examples given, I disagree with this when one of the conditional branches is considerably longer than the other. I find it far better to place the shortest branch body first, this gets that condition out of the way and avoids having any “hidden” else dangling around at the end of the if. Such an else may require some scrolling to discover what if the else belongs to, and can be easily missed when reading the if.

The principle I try to follow is to get as much logic “resolved” and out of the way (i.e. don’t need to continue to keep mental track of it) in the fewest possible lines.

e.g.

if (a) {
  // some lengthy logic, ignore content
  for (let i = 0; i < items.length; i++) {
    result += items[i]
  }
  for (let i = 0, token; (token = tokens[i]); i++) {
    const token = tokens[i]
    result += token
  }
  items.forEach((item) => {
    result += item
  })
  return result
} else {
  console.log(a) // what if does this belong to again?
}

vs

if (!a) {
   console.log(a) // easy to see what conditional this belongs to. else is now done & out of the way.
} else {
  // some lengthy logic, ignore content
  for (let i = 0; i < items.length; i++) {
    result += items[i]
  }
  for (let i = 0, token; (token = tokens[i]); i++) {
    const token = tokens[i]
    result += token
  }
  items.forEach((item) => {
    result += item
  })
  return result
}

[timoxley]

It works incredibly well at preventing indentation blowout too when resolving it with early exits etc.

https://youtu.be/_wO8toxinoc?t=145