Undefined Symbol

The linter can do a much better job of detecting problems if it knows which globals a piece of code uses. If you see warnings like

ERROR: foo.js:10+33 - 39: Symbol i has not been defined
    return arr[i];
then it's possible you're missing a var declaration or have misspelled the name of the variable.

If you meant to use a global, just put a comment at the top of the file listing the globals you depend upon.

/** @requires window */

As always, to turn this off, put the error message name UNDEFINED_SYMBOL in the ignores list.