Fix: Use ts utilities function to determine variable type (#136)

[soda0289]

This fixes issue an where an async function would mark all variable declarations as constant. It uses the isConst and isLet functions from TypeScript compiler utilities file.

Fixes #136

[eslintbot]

Thanks for the pull request, @soda0289! I took a look to make sure it's ready for merging and found some changes are needed:

• Pull requests with code require an issue to be mentioned at the end of the commit summary, such as (fixes #1234). Please update the commit summary with an issue (file a new issue if one doesn't already exist).

Can you please update the pull request to address these?

(More information can be found in our pull request guide.)

[eslintbot]

LGTM

[JamesHenry]

Thanks a lot for this, @soda0289!

Can we please abstract this into a helper function similar to the following:

/**
 * Returns the declaration kind of the given TSNode
 * @param  {TSNode}  node TypeScript AST node
 * @returns {string}     declaration kind
 */
function getDeclarationKind(node) {
    if (node.kind === SyntaxKind.TypeAliasDeclaration) {
        return "type";
    }
    switch (true) {
        case ts.isLet(node):
            return "let";
        case ts.isConst(node):
            return "const";
        default:
            return "var";
    }
}

...and then make use of getDeclarationKind for all three of the relevant cases:

• SyntaxKind.VariableStatement (kind: getDeclarationKind(node.declarationList))

• SyntaxKind.VariableDeclarationList (kind: getDeclarationKind(node))

• SyntaxKind.TypeAliasDeclaration (kind: getDeclarationKind(node))

Very minor point, but as there are changes to be made anyway, please can we go for async-function-with-var-declaration as the test name

[JamesHenry]

@soda0289 Please be sure to rebase against master before making those changes, a PR was just merged that also touches one of those cases

[eslintbot]

LGTM

[soda0289]

@JamesHenry
I created a separate function for determining declaration kind and renamed the test.