Add new method to check if node is null or not

[danez]

Q	A
Fixed Issues?
Patch: Bug Fix?	n
Major: Breaking Change?	n
Minor: New Feature?	y
Tests Added + Pass?	Yes
Documentation PR Link
Any Dependency Changes?	n
License	MIT

While using babel traverse in a typescript project I stumbled upon an annoyance that I wasn't able to really fix in my code, besides defining the types for every single path manually.

The code looks like this:

function xyz(path: NodePath): void {
  if (path.isArrayExpression()) {
    path.get('elements').map(elementPath => {
      // elementPath: NodePath<Expression | SpreadElement | null>
      if (elementPath.node === null) return;
      otherFunc(elementPath as NodePath<Expression | SpreadElement>); // Have to define that because null is not possible anymore.
    });
  }
}

With the introduction of the new method it can be simplified to this, because TS now can figure out itself that node is not null anymore:

function xyz(path: NodePath): void {
  if (path.isArrayExpression()) {
    path.get('elements').map(elementPath => {
      // elementPath: NodePath<Expression | SpreadElement | null>
      if (!elementPath.hasNode()) return;
      otherFunc(elementPath);
    });
  }
}

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[nicolo-ribaudo]

I wonder why the type refinement in your example doesn't work; it seems to work in simpler cases 🤔
https://www.typescriptlang.org/play?ts=4.4.4#code/MYGwhgzhAEByD2ATApgBTAFwBYB4AqAfNAN4BQ0F0AdksgIQBc0eA3KQL6mkYCeADsmb9kAQWgBeEtF4CmAIhFzo7NjMF5hAIQlS18zUpVdkADz7wAThmgAzAK5VgGAJbwq0AObIMCFBoEAFHyYWEy+aCE4VHYgINAAPkICYon+yJoEAJRMEBgWzl

EDIT: Oh ok, it doesn't work if you use path rather than path.node.*.