在包含promise的for循环中的词法作用域？ [英] Lexical scoping in a for loop enclosing a promise?

问题描述

我有一个 ids 对象，它将 id 字符串映射到 c $ c>对象。

I have an ids object, which maps id strings to product objects.

for id of ids
  product = ids[id]
  console.log product # Prints out something different each loop. :)
  Product.create(product).then ->
    console.log product # Only prints out the last id each loop. :(

我使用库进行数据库交互，我试图在中打印出产品变量，然后 code>函数，但是我只是在 ids 中找到最后的 id 这是一个范围问题我如何适当地范围产品变量，以便它打印出一个不同的产品在然后函数每个循环？

I'm using a library for database interactions, which exposes promises (indicated by the then function above). I'm trying to print out the product variable inside the then function, but I only seem to be getting the last id in ids, so it looks like it's a scoping issue. How can I scope the product variable properly so that it prints out a different product in the then function each loop?

推荐答案

@false确实找到产品

@false did find the right duplicate describing your issue. Indeed, you've got a scoping issue where product is non-local to the loop body, and you get the last item only from your asynchronous callbacks.

如何区分产品变量

在惯用coffeescript中，您将使用 do 符号：

In idiomatic coffeescript, you will use the do notation for the IEFE in the loop:

for id of ids
  do (product = ids[id]) ->
    console.log product
    Product.create(product).then ->
      console.log product

或者，直接从 of -loop：

Or, drawing the property value directly from the of-loop:

for id, product of ids
  do (product) ->
    …

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