为什么console.log没有显示任何内容？

Question

I have a map function, which brings me a lot of strings with different values in some cases (before the map function, I also have a filter function too). 1st: I'm sure the returns are strings, since I console.log(typeof thing.name) and it returns me, well, strings.

In some cases it brings me a lot of strings and in another cases it me brings me nothing, since the return depends on the filter.

The problem is: when the filter brings me no results, the console log do not print anything. I know, it makes sense. But I'm trying to make a conditional which returns me something like "undefined, null, false/true" when filter returns me 0/none/nothing results. It is possible?

I have something like that:

filteredOffers.map(offer => {
  if(offer.name === "" || offer.name === null || offer.name === undefined) {
    console.log("Test test test")
  } else {
    return (
      <p>{offer.name}</p>
    )
  }
})

Answer 1

Your question is

Why console.log shows me nothing?

And in your question you say

when the filter brings me no results, the console log do not print anything

Where is what is happening.

.filter will return a new array with only the elements of the array that have passed some condition and returned true . If no conditions are true, it will return an empty array ( [] ).

.map will loop throgh an array and return something in this new array, if it's an empty array, .map won't run an just return that empty array.

When you say when the filter brings me no results it means that .filter returned an empty array and when you do [].map(...) , the function inside .map won't run and it will just return [] .

That answers Why console.log shows me nothing? , you are doing [].map(...) and the function never runs.

Answer 2

testing

!offer.name

will return true when

• offer.name is undefined
• offer.name is null
• offer.name is false
• offer.name is the empty string ('')
• offer.name is 0

so you might want to filter your offers as follow

filteredOffers.filter(offer => !!offer.name)

and only then map the output

filteredOffers.filter(offer => !!offer.name).map(offer => (<p>{offer.name}</p>))