外部函数返回一个内部函数，可以访问外部函数的值

I need to create a function which I will pass to my database server. The returned function will take a single item as a parameter and compare that item to a list of requirements.

我需要创建一个函数,我将传递给我的数据库服务器。返回的函数将单个项目作为参数,并将该项目与需求列表进行比较。

For this I need a function generating function that takes an array as it's argument and returns the inner function which has that array built in to it.

为此我需要一个函数生成函数,它接受一个数组作为它的参数,并返回内置函数,该函数内置了该数组。

Here's an example:

这是一个例子:

function create_query (list_of_requirements) {
  return function (item) {
    var is_match = true
    // the next function sets is_match to false if the item fails
    list_of_requirements.forEach(check_if_item_meets_requirement)
    return is_match
  }
}

An example of using this:

使用此示例:

function search (parsed_user_string) {
  db.get(create_query(parsed_user_string)).then(function(results){
    show_results(results)
  })
}

How can I build the list of requirements into the inner function?

如何在内部函数中构建需求列表?

1 个解决方案

#1

I needed to use a closure.

我需要使用一个闭包。

Here's a simpler example of a solution.

这是一个更简单的解决方案示例。

function makePrinter (num) {
  (return function () {
    print(num)
    })
}

and then:

var print5 = makePrinter(5)
print5() > prints 5!

I still don't quite get how closures accomplish this, but there it is.

我仍然不太明白闭包是如何实现这一目标的,但事实确实如此。

#1