Better Errors

[brigand]

I'm working on a project where it generates AST based on an external data source (specification -> js ast -> js code). I get errors like this:

TypeError: Cannot read property 'type' of undefined
    at generateStatement (/.../my-project/node_modules/escodegen/escodegen.js:1557:21)
    at /.../my-project/node_modules/escodegen/escodegen.js:1563:42
    at withIndent (/.../my-project/node_modules/escodegen/escodegen.js:564:21)
    at generateStatement (/.../my-project/node_modules/escodegen/escodegen.js:1561:13)
    at maybeBlock (/.../my-project/node_modules/escodegen/escodegen.js:717:28)
    at generateFunctionBody (/.../my-project/node_modules/escodegen/escodegen.js:826:25)
    at generateExpression (/.../my-project/node_modules/escodegen/escodegen.js:1195:27)
    at generateExpression (/.../my-project/node_modules/escodegen/escodegen.js:918:21)
    at generateStatement (/.../my-project/node_modules/escodegen/escodegen.js:1661:23)
    at generateStatement (/.../my-project/node_modules/escodegen/escodegen.js:1955:21)

It'd be good to include some kind of message explaining where the error is. This could be done with a recursive stack. When you recurse, push the key onto the stack (e.g. "0" or "expression"). When you exit a level of recursion, pop an item from the stack.

If the code is wrapped in a try/catch, you can then look at the stack and console.log("Error at " + stack.join('.')), and rethrow the error.

Now the error would look like this, which I can resolve by hand or with an extract function.

Error at 0.body.body.0.left
TypeError: Cannot read property 'type' of undefined
    at generateStatement (/.../my-project/node_modules/escodegen/escodegen.js:1557:21)