Fund: Rule proposal: `prefer-else-if`

Fail

if (foo === '1') {
  // ...
}
if (foo === '2') {
  // ...
}

function a() {
  if (foo === '1') {
    // ...
    return;
  }

  if (foo === '2') {
    // ...
    return;
  }
}

if (foo === '1') {
  // ...
} else if (foo === '2') {
  // ...
}

Original proposal for `prefer-switch`

if (foo === '1') {
  ...
}
if (foo === '2') {
  ...
}
if (foo === '3') {
  ...
}
if (foo === '4') {
  ...
}

To fix this case, we can simply only check if foo is declared as const.

This come from my work, but real case is more complicated, it's like

if (foo.bar === '1') {
  ...
}
if (foo.bar === '2') {
  ...
}
if (foo.bar === '3') {
  ...
}
if (foo.bar === '4') {
  ...
}

To fix this case, we need to check foo.bar and foo didn't get changed in each if block, I feel this is hard (even impossible) to do.