NodeJS回调中shop变量未定义问题的解决方案咨询

Hey there, let's break down what's going wrong here and fix it step by step!

First, there are two key issues causing your problem:

1. Typo: You're looping over shop.collections (plural), but inside the loop you wrote shop.collection[i] (singular). This will directly lead to a "property not found" error, which might make you mistakenly think shop is undefined.
2. Closure Trap: The i declared with var is a function-scoped variable—all iterations of the loop share the same i. Since myOwnService.createCollection is asynchronous, by the time its callback runs, the loop has already finished, and i equals shop.collections.length. At that point, shop.collections[i] becomes undefined, which also messes up your access to shop-related properties.

Here are two solid fixes to resolve this:

Solution 1: Replace var with let to use block scoping #

let creates a separate scope for each loop iteration, so the callback will get the correct index value when it executes:

for(let i=0; i < shop.collections.length; i++){ 
  if(!shop.collections[i].active){ 
    const data = { 
      "name": shop.collections[i].name, 
      "visible": true 
    }; 
    myOwnService.createCollection(data, accessToken, function(err, response, body){ 
      if (!err) { // Don't forget error handling to avoid new bugs
        shop.collections[i].serviceId = body.id; 
      }
    }) 
  } 
}

Solution 2: Use forEach to avoid closure issues entirely #

The forEach callback creates an independent scope for each element. You can directly use the current collection object, no need to worry about index problems at all:

shop.collections.forEach(function(collection) {
  if(!collection.active){ 
    const data = { 
      "name": collection.name, 
      "visible": true 
    }; 
    myOwnService.createCollection(data, accessToken, function(err, response, body){ 
      if (!err) {
        collection.serviceId = body.id; 
      }
    }) 
  }
});

A quick extra tip: Always add error handling (like the if (!err) checks above). If the createCollection request fails, body might be undefined, which would cause another set of errors.

内容的提问来源于stack exchange，提问作者NVO