TypeError: Cannot read property '_walk' of null

[Crashthatch]

Bug report

Uglify fails to minify some code and instead errors with the above error. Seems to be affecting several people using uglify, but I couldn't see an open issue in this repo, so thought I'd bring it to your attention / open this issue to track.

terser/terser#120
ember-cli/ember-cli#8075
angular/angular-cli#12414

There was an old bug from 2017 which was supposedly fixed with the same error message:
#1609

Happens when running uglify from the CLI or through uglifyjs-webpack-plugin

Running with --keep-fnames or adding collapse_vars to the compress webpack config options works around the issue:

        new UglifyJsPlugin({
          uglifyOptions: {
            compress: {
              collapse_vars: false
            },
          }
        })

Uglify version (uglifyjs -V)
3.4.9
(Also tested with 3.3.28 & a few in between, they all error)

JavaScript input

I can't share my company's code, see terser/terser#120 (comment) for a reproducible example.

The uglifyjs CLI command executed or minify() options used.
../../node_modules/.bin/uglifyjs --compress --verbose client-6a7cff1a.js

JavaScript output or error produced.
...<hundreds of warnings because I used --verbose>
WARN: Dropping unused variable gpu [client-6a7cff1a.js:59688,12]
WARN: Dropping unused variable retina [client-6a7cff1a.js:59710,16]
WARN: Collapsing fe [client-6a7cff1a.js:59777,19]
WARN: Dropping unused variable fe [client-6a7cff1a.js:59776,16]
WARN: Collapsing d [client-6a7cff1a.js:59776,21]
WARN: Collapsing e [client-6a7cff1a.js:59775,20]
ERROR: Cannot read property '_walk' of null
at AST_Dot.eval (eval at (/path/to/my/project/node_modules/uglify-js/tools/node.js:21:1), :873:29)
at TreeWalker._visit (eval at (/path/to/my/project/node_modules/uglify-js/tools/node.js:21:1), :1151:21)
at AST_Dot._walk (eval at (/path/to/my/project/node_modules/uglify-js/tools/node.js:21:1), :872:24)
at AST_VarDef.eval (eval at (/path/to/my/project/node_modules/uglify-js/tools/node.js:21:1), :820:40)
at TreeWalker._visit (eval at (/path/to/my/project/node_modules/uglify-js/tools/node.js:21:1), :1151:21)
at AST_VarDef._walk (eval at (/path/to/my/project/node_modules/uglify-js/tools/node.js:21:1), :818:24)
at AST_Var.eval (eval at (/path/to/my/project/node_modules/uglify-js/tools/node.js:21:1), :801:32)
at TreeWalker._visit (eval at (/path/to/my/project/node_modules/uglify-js/tools/node.js:21:1), :1151:21)
at AST_Var._walk (eval at (/path/to/my/project/node_modules/uglify-js/tools/node.js:21:1), :798:24)
at walk_body (eval at (/path/to/my/project/node_modules/uglify-js/tools/node.js:21:1), :448:17)

[ersel]

We're experiencing the same problem because we depend on tether library. Here is a minimal example:

var xyz = function() {
  var isFullscreenElement = function isFullscreenElement(e) {
    var d = e.ownerDocument;
    var fe = d.fullscreenElement || d.somethingElse
    return fe === e;
  };

  var currentNode = null;
  while(isFullscreenElement(currentNode)){}
}

[ersel]

this variation works:

var xyz = function() {
  var d;
  var isFullscreenElement = function isFullscreenElement(e) {
    d = e.ownerDocument;
    var fe = d.fullscreenElement && d.somethingElse
    return fe 
  };

  var currentNode = null;
  while(isFullscreenElement(currentNode)){}
}

something to do with closures maybe?

[rjksn]

How do we fix this… if we're just using Gulp?

[kaii-zen]

stream.pipe(uglify({ keep_fnames: true }))

if you don't mind your function names not being obfuscated.

[ersel]

we made the following config change collapse_vars: false

[NatarajanGanapathi-Hexaware]

We are getting the following issue when minify the mysql2 package. I recorded this issue in mysql2 also.

node-mysql2 Issue 899

node_modules/mysql2/lib/commands/index.js []
TypeError: Cannot read property 'replace' of undefined
    at make_string (eval at <anonymous> (/Users/NatarajanG/BitBucket/mission/mission.shrink/node_modules/uglify-es/tools/node.js:21:1), <anonymous>:5645:19)
    at encode_string (eval at <anonymous> (/Users/NatarajanG/BitBucket/mission/mission.shrink/node_modules/uglify-es/tools/node.js:21:1), <anonymous>:5689:19)
    at Object.print_string (eval at <anonymous> (/Users/NatarajanG/BitBucket/mission/mission.shrink/node_modules/uglify-es/tools/node.js:21:1), <anonymous>:6107:27)
    at eval (eval at <anonymous> (/Users/NatarajanG/BitBucket/mission/mission.shrink/node_modules/uglify-es/tools/node.js:21:1), <anonymous>:6396:16)
    at doit (eval at <anonymous> (/Users/NatarajanG/BitBucket/mission/mission.shrink/node_modules/uglify-es/tools/node.js:21:1), <anonymous>:6168:13)
    at AST_Directive.eval (eval at <anonymous> (/Users/NatarajanG/BitBucket/mission/mission.shrink/node_modules/uglify-es/tools/node.js:21:1), <anonymous>:6175:13)
    at eval (eval at <anonymous> (/Users/NatarajanG/BitBucket/mission/mission.shrink/node_modules/uglify-es/tools/node.js:21:1), <anonymous>:6438:22)
    at Array.forEach (<anonymous>)
    at display_body (eval at <anonymous> (/Users/NatarajanG/BitBucket/mission/mission.shrink/node_modules/uglify-es/tools/node.js:21:1), <anonymous>:6429:14)
    at eval (eval at <anonymous> (/Users/NatarajanG/BitBucket/mission/mission.shrink/node_modules/uglify-es/tools/node.js:21:1), <anonymous>:6463:9) []
node_modules/mysql2/lib/commands/ping.js []

[EmberRed]

same code work for a project and not for the other...
gulp 4.0
error:
Message:
Cannot read property 'minify' of undefined
Details:
domainEmitter: [object Object]
domain: [object Object]
domainThrown: false
any ideas?