如何枚举模块中的包依赖关系？

Question

Guys i've been coding an node_module that's gives you the dependencies of the module you choose, So there is my code

function depend(modulename, cb) {
let package = JSON.parse(fs.readFileSync("./node_modules/"+modulename+'/package.json', "utf8"));
var re = 'CHECKING' ? package.dependencies : 'The module has no dependencies';
cb(re)  
}

const fs = require('fs');

module.exports = depend;

When i run it it on a module has no modules its gives me {} Instead of The module has no dependencies , So any ideas?

Answer 1

I'd suggest taking a look at how the Ternary (conditional) Operator works.

In reference to the code you posted a comment:

Your current code simply checks for the existence of package.dependencies, which even if it is an empty object, something like if(package.dependencies)... will evaluate to true because an empty object is a truthy value.

What you need to do is check if the object itself is empty. One way to do that is to check the length of its keys by using Object.keys .

var re = Object.keys(package.dependencies).length ? package.dependencies : 'The module has no dependencies';

But an even better check would be a combination of your approach and this one:

var re = package.dependencies && Object.keys(package.dependencies).length ? ...

As it checks for both the existence of package.dependencies as well as whether or not it is empty.

Answer 2

var re = 'CHECKING' ? package.dependencies : 'The module has no dependencies'; is a ternary .

Here it means :

If 'CHECKING' then assign package.dependencies to re otherwise assign 'The module has no dependencies' to re

This is your error, if ('CHECKING') will always evaluate to true so it will always assign package.dependencies to re . You'll have to refactor your code to something like this :

var re = Object.keys(package.dependencies).length > 0 ? package.dependencies : 'The module has no dependencies';

Which will test if package.dependencies have one or more dependencies in order to affect the correct value to re . We don't use length on package.dependencies because it is an object which haven't any length property, instead we use Object.keys .

In the second example you provided in the comments, if (package.dependencies) will also always evaluate to true because package.dependencies is not null or undefined, so it's considered to be true .