在Node.js中导出模块时的依赖关系范围

Question

When exporting a module that has another dependency, is it best to include that dependency within the module export function or outside of it? I usually see the latter, but it seems like it would be best to keep it in the local scope.

For example:

var foo = require('foo');

module.exports = function(d) {
    return foo(d)/2;
}

vs.

module.exports = function(d) {
    var foo = require('foo');

    return foo(d)/2;
}

Answer 1

Only things exposed on module.exports and global can be accessed from other modules in node. Unlike in the browser, var creates a local reference. To quote from node's documentation :

In browsers, the top-level scope is the global scope. That means that in browsers if you're in the global scope var something will define a global variable. In Node this is different. The top-level scope is not the global scope; var something inside a Node module will be local to that module .

The difference between the two versions is therefore minimal - the first incurs a lookup in the local scope, while the other hits require.cache every time the function is invoked. From what I have seen of node code, the former ( var someVar = require('something'); ) seems to be preferred.