Error in atom package ternjs

Question

For web development (and more), my favorite editor is the great atom editor, the open source project by github.

Like many code editors, we can extend it by installing a lot of plugins. Among others, I use atom-ternjs:

Javascript code intelligence for atom with tern.js. Uses suggestion provider by autocomplete-plus.

Today I get this error into a 'alert styled' flash message box in the editor window's top right corner:

TypeError: Cannot read property 'CallExpression' of undefined at findTypeFromContext.NewExpression (/home/poremil/.atom/packages/atom-ternjs/node_modules/tern/lib/infer.js:1588:18) at Object.exports.typeFromContext (/home/poremil/.atom/packages/atom-ternjs/node_modules/tern/lib/infer.js:1623:24) at Object.findCompletions [as run] (/home/poremil/.atom/packages/atom-ternjs/node_modules/tern/lib/tern.js:684:23) at run (/home/poremil/.atom/packages/atom-ternjs/node_modules/tern/lib/tern.js:218:30) at Object.exports.withContext (/home/poremil/.atom/packages/atom-ternjs/node_modules/tern/lib/infer.js:774:18) at /home/poremil/.atom/packages/atom-ternjs/node_modules/tern/lib/tern.js:225:13 at analyzeAll (/home/poremil/.atom/packages/atom-ternjs/node_modules/tern/lib/tern.js:339:15) at doRequest (/home/poremil/.atom/packages/atom-ternjs/node_modules/tern/lib/tern.js:209:5) at Object.signal.mixin.request (/home/poremil/.atom/packages/atom-ternjs/node_modules/tern/lib/tern.js:149:7) at respond (/home/poremil/.atom/packages/atom-ternjs/node_modules/tern/bin/tern:224:10)

However, a didn't notice any specific bug in my workflow. That said, I would want to understand what happend.

I also opened an issue on the github project

Answer 1

Yes, this does look like a bug. Here is a simplified extract from the breaking code:

var findTypeFromContext = {
  NewExpression: function() { return this.CallExpression() }
  ,CallExpression: function() { console.log('calling expression'); }
}
var finder = findTypeFromContext['NewExpression'];
finder();

This breaks because of the this keyword.

1. The var finder = findTypeFromContext['NewExpression']; assignment takes NewExpression method "out" (detaching from the parent object).
2. By this assignment the this keyword now points to the current parent object - where CallExpression does not exists.

My quick-fix would be to immediately call the function on the object so this is still pointing at the right place:

var findTypeFromContext = {
  NewExpression: function() { this.CallExpression() }
  ,CallExpression: function() { console.log('calling expression'); }
}
findTypeFromContext['NewExpression']();