The only reason to use typeof foo === "undefined" is when foo is a
global identifier that might not have been declared at all, so it
might raise a ReferenceError if evaluated. For a variable declared
with const or let or import, a function argument, or a complex
expression, simply foo === undefined is equivalent.
Some of these conditions have become impossible and can be removed
entirely, and some can be replaced more idiomatically with default
parameters (note that JavaScript does not share the Python misfeature
of evaluating the default parameter at function declaration time).
Signed-off-by: Anders Kaseorg <anders@zulip.com>
Instead of prohibiting ‘return undefined’ (#8669), we require that a
function must return an explicit value always or never. This prevents
you from forgetting to return a value in some cases. It will also be
important for TypeScript, which distinguishes between undefined and
void.
Signed-off-by: Anders Kaseorg <anders@zulip.com>
ES and TypeScript modules are strict by default and don’t need this
directive. ESLint will remind us to add it to new CommonJS files and
remove it from ES and TypeScript modules.
Signed-off-by: Anders Kaseorg <anders@zulip.com>
This commit was originally automatically generated using `tools/lint
--only=eslint --fix`. It was then modified by tabbott to contain only
changes to a set of files that are unlikely to result in significant
merge conflicts with any open pull request, excluding about 20 files.
His plan is to merge the remaining changes with more precise care,
potentially involving merging parts of conflicting pull requests
before running the `eslint --fix` operation.
Signed-off-by: Anders Kaseorg <anders@zulipchat.com>
ESLint won’t convert these automatically because it can’t rule out a
behavior difference arising from an access to a self-referential var
before it’s initialized:
> var x = (f => f())(() => x);
undefined
> let y = (f => f())(() => y);
Thrown:
ReferenceError: Cannot access 'y' before initialization
at repl:1:26
at repl:1:15
Signed-off-by: Anders Kaseorg <anders@zulipchat.com>
With webpack, variables declared in each file are already file-local
(Global variables need to be explicitly exported), so these IIFEs are
no longer needed.
Signed-off-by: Anders Kaseorg <andersk@mit.edu>
This commit prepares the frontend code to be consumed by webpack.
It is a hack: In theory, modules should be declaring and importing the
modules they depend on and the globals they expose directly.
However, that requires significant per-module work, which we don't
really want to block moving our toolchain to webpack on.
So we expose the modules by setting window.varName = varName; as
needed in the js files.
Also adds a custom rule to eslint. Since the recommended way of extending
eslint is to create plugins as standalone npm packages, the separate rule
is published as 'eslint-plugins-empty-returns'.
Fixes#8669.
Anders Kaseorg
Anders Kaseorg
Armaan Ahluwalia
Rohitt Vashishtha
Umair Khan
Brock Whittaker
Rafid Aslam
Leo Franchi