Polymer js minifier reusing catch error variable inside catch block

[nachoab]

Description

This is an error of the js minifier. When the error variable is not used inside the catch statement, it is renaming it to "a", but if a variable is created inside the catch block it is also using "a". In case of const variables this throws an error because "a" has already been declared.

Versions & Environment

• Polymer CLI: 1.6.0
• node: 8.7.0
• Operating System: mac os 10.13

Steps to Reproduce

Minify this code:

try {
    // something
 } catch(e) {
    const date = new Date();
    console.log(date);
}

Expected Results

try {
    // something
} catch (a) {
    const e = new Date();
    console.log(e);
}

Actual Results

try {
    // something
} catch (a) {
    const a = new Date();
    console.log(a);
}

If the error variable is used, then it is correctly minified.

[nachoab]

Another uglify error.

Here "bar" can be ignored because it is never used:

async function example() {
  var foo, bar;
  try {
    [foo, bar] = await Promise.all([req(1), req(2)]);
  } catch(e) {}
  console.log(foo);
}

but the minifier ignores "foo" too:

async function example() {
  var a;
  try {
      await Promise.all([req(1), req(2)])
  } catch (a) {}
  console.log(a)
}

If both "foo" and "bar" were used, the minifier does its job well:

async function example() {
  var foo, bar;
  try {
    [foo, bar] = await Promise.all([req(1), req(2)]);
  } catch(e) {}
  console.log(foo, bar);
}

which is minified to:

async function example() {
  var a, b;
  try {
      [a, b] = await Promise.all([req(1), req(2)])
  } catch (a) {}
  console.log(a, b)
}

[nachoab]

Here goes another one:

Input:

function example(obj) {
  if (!!obj.foo || obj.bar) {
    return true;
  }
  return false;
}

Actual Result, which is not the same, it doesn't return a boolean:

function example(a){
  return!!a.foo||a.bar
}

Expected Result, for instance:

function example(a){
  return!!(!!a.foo||a.bar)
}

[justinfagnani]

@nachoab the current pre-release of the CLI includes some updated Babel packages, that may or may not effect this. Could you try npm i -g polymer@next and see if this still happens?

For your first example at least, it seems like the version of Babel minify that the Babel REPL uses isn't exhibiting the bug: https://babeljs.io/repl/#?babili=true&browsers=&build=&builtIns=false&code_lz=C4JwngBA3gUB8QPSIgZwPYFsCmwAWAlgHYDmcAvhAMYCGwVeAFNgJTRwJXpGrAQAmdbBAC8EItgDuEACJDGLANwd4XHugA22AHQb0JRoOCtl5IA&debug=false&forceAllTransforms=false&shippedProposals=false&circleciRepo=&evaluate=false&fileSize=false&lineWrap=false&presets=babili&prettier=false&targets=&version=6.26.0&envVersion=

[justinfagnani]

The last one I think we'll need to file a Babel bug for: https://babeljs.io/repl/#?babili=true&browsers=&build=&builtIns=false&code_lz=GYVwdgxgLglg9mABAUwB4EMC2AHANsgCjgCMArASkQG8AoRRGYRAgQhZNIDpg45EAffog6di6AE6Va9euORQQ4pFHEhkAbjqIAvlrkKliYOlwBnDTW1A&debug=false&forceAllTransforms=false&shippedProposals=false&circleciRepo=&evaluate=false&fileSize=false&lineWrap=false&presets=babili&prettier=false&targets=&version=6.26.0&envVersion=

[nachoab]

The last one is fixed too in the polymer@next version:

function example(a){return!(!a.foo&&!a.bar)}

The second one is still failing: https://babeljs.io/repl/#?babili=true&browsers=&build=&builtIns=false&code_lz=IYZwngdgxgBAZgV2gFwJYHsIwKYA9gC2ADgDbYAUAlDAN4BQMMAbsAE7zroA0MARmwG4GMZKzC1hjANpxOPfqwC6MALwxgAd2CpkMAAqt0BVCGwA6YCRLkprbAEdyARko87jgEyVFlIYwC-MFDAyFAAFuTY1DT-wlCYIOhkZiToAObksui-dP5AA&debug=false&forceAllTransforms=false&shippedProposals=false&circleciRepo=&evaluate=false&fileSize=false&lineWrap=false&presets=babili&prettier=false&targets=&version=6.26.0&envVersion=

[stale[bot]]

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