Check to see if dynamic import is a module in JavaScript/TypeScript-CodePudding

I am working on a ScriptManager class for a project that was created many years ago. The original code read scripts from a database, and these scripts are different depending on the customer and installation (the application is a desktop app that uses Chrome Embedded Framework to display web pages). The code would read custom JavaScript code and eval() it, which of course is highly undesirable.

I am replacing this code with a ScriptManager class that can support dynamically inserted code, and the ScriptManager is capable of loading code as a module using JavaScript's dynamic import() command, or loading code as pure script by creating a script tag dynamically in the document.

My problem is that there are many different possible custom code blocks in the database, and not all are modules; some will be pure script until those can be converted to modules at a later time. My code can handle this as described above, but I need a way to detect if the script code from the database is a module, so I can either use the import() command or insert a script tag if it is not.

I am solving this temporarily by making sure any module script code has "export const isModule = true", and checking this after calling import(). This works, but any code that is pure script still results in a module variable, but with no exports in it. If possible I don't want the other developers to have to remember to add isModule = true to any modules they develop in the future.

Is there a way to check that code is a module without having to do complex analysis of the code to check if there are exports in it? Since import() still returns an object and throws no errors if there are no exports, I don't know how to detect this.

CodePudding user response：

So if you look here How can I tell if a particular module is a CommonJS module or an ES6 module? you will see I answered a similar question.

So the thing is Sarah, modules are defined by the way that they resolve. Module-types resolving differently is what, not only makes them incompatible with one another, but it is also why we name them differently. Originally Transpillers like Babel & TypeScript were invented because of differences in ECMA-262 Specifications, and the desire to support people who didn't have the updated specifications, as well as supporting the newer features for those who did.

Today transpilers are still being used, conceptually, much the same way. They still help us maintain a single code base while supporting older specifications, and features in newer specifications, at the same time, but the also have the added benefit of being able to generate multiple different builds from a single code base. They use this to support different module types. In node.js, the primary module-type is CJS, but the future lies in ESM modules, so package maintainers have opted to dual build the projects. The use the TypeScript Compiler (aka Transpiler) to emit a CJS build, and an ESM build.

Now this is where things get complicated, because you cannot tell just by looking at a module if it CJS or ESM in this situation, **you absolutely have to inspect its code, and check if it has more than one tsconfig.json file (because it would need at-least 2 to maintain a bi-modular build (which are becoming increasingly common with the turn of each day)

My Suggestion to You:

Use well documented packages. Good packages should be documented well, and those packages should state in their README.md document, what type of package/module they are, and if the package supports more than one module type. If in doubt you can either come and ask here, or better yet, you can ask the maintainer by creating an issue, asking them to add that information to their README.md document.

CodePudding user response：

You can check that there are no export after import. In chrome import() added empty default for non module.

function isNotModule(module) {
    return (!Object.keys(module).length) || (!!module.default && typeof module.default === 'object' && !Object.keys(module.default).length)
}

import('./test.js')
    .then((module) => {
        console.log('./test.js',isNotModule(module))
    })

May be it's better to check source code via regex to check if it contains export

something like this

const reg = new RegExp('([^\w]|^)export((\s )\w|(\s*{))')
reg.test(source)