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Idea: extend capability of `extract-sequence-expressions` or applicable rule

See original GitHub issue

One class of sequence expressions missed by the extract-sequence-expressions rule (or some other rule for this purpose) is when the sequence statements are tucked into an "if expression’. For example:

let a = true;

if(console.log('one'), console.log('two'), a) {

This is equivalent and more clearly written as:

let a = true;


if (a) {

Javascript returns the last expression in the sequence for evaluation in the “if expression”.

Issue Analytics

  • State:closed
  • Created 9 months ago
  • Comments:8 (4 by maintainers)

github_iconTop GitHub Comments

eprestoncommented, Dec 30, 2022

It works well.

I’m going to write out some detailed bits so we have a good record of test overage, environment, versions.

Tested Versions

module version
putout “28.3.0”
@putout/plugin-extract-sequence-expressions “3.5.0”
@putout/plugin-logical-expressions “1.2.0”

Test Project Metrics

language files code comment blank total
JavaScript 283 50,763 2,617 6,566 59,946

Test Detection

94 errors in 50 files

Test Detail

Test 1:

  • It hoists the sequence expressions found in 'if statements" correctly
  • this is the simple case found above

Test 2:

  • When it is proceeded by a single line, left associating control statement with an optional BodyBlock
  • It creates a BodyBlock if required, then hoists the sequence statements above leaving the condition
  • preserves execution order and practical outcomes
  • exposes the actual execution of the code by the runtime while improving readability

“For Statement” example for clarity:

for (let n = 0; n < t.length; n++)
  if (((i = '(' + e + ': ' + t[n] + ')'), window.matchMedia(i).matches)) return t[n];

Is transformed into the more readable equivalent:

for (let n = 0; n < t.length; n++) {
  i = '(' + e + ': ' + t[n] + ')';
  if (window.matchMedia(i).matches) return t[n];
coderaisercommented, Dec 28, 2022

I’d be excited to see if we can hoist out these sequence expressions. Helpful if someone puts a comma in the wrong place creating a sequence expression when they mean to combine a condition into a larger expression for the control block. It would be neat to hit save and see the statement get ejected above on its own line.

Landed in @putout/plugin-extract-sequence-expressions@3.5.0 🎉. Is it works for you?

Read more comments on GitHub >

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