CODEWITHSUNDEEP
javascriptnode.jslodash
brineon
brineon

Reputation: 123

How to filter a list using lodash if the filter function is asynchronous

I am new to lodash and Javascript in general. I am using nodejs. I am using the lodash filter function to filter some contents in my collection.

Here is the snippet

filteredrows = _.filter(rows, function(row, index){

   //here I need to call some asynchronous function which checks the row
   //the return value of this asynchronous function will determine whether to return true or false for the filter function.

});

My question is, how do I do this? using a closure? Is it possible to do this within the lodash filter function? Thanks in advance.

Upvotes: 12

Views: 9212

Answers (3)

clifdensprit
clifdensprit

Reputation: 4901

If you want to accomplish this with lodash instead of installing a new library(async) you can do the following:

const rowFilterPredicate = async (row, index) => {

  // here I need to call some asynchronous function which checks the row
  // the return value of this asynchronous function will determine whether to return true or false for the filter function.

}

// First use Promise.all to get the resolved result of your predicate
const filterPredicateResults = await Promise.all(_.map(rows, rowFilterPredicate));

filteredrows = _.chain(rows)
  .zip(filterPredicateResults) // match those predicate results to the rows
  .filter(1) // filter based on the predicate results
  .map(0) // map to just the row values
  .value(); // get the result of the chain (filtered array of rows)

Upvotes: 1

Cristian Agudelo
Cristian Agudelo

Reputation: 627

Lodash isn't an asyncronous tool. It makes filtering information in realtime veery fast. When you need to make a process asynchronous, you must use bluebird, Async, Native promises or callbacks.

I think that you should use Lodash and Underscore, only to organize Objectdata in realtime.

Upvotes: 0

000
000

Reputation: 27247

lodash may not be the best tool for this job. I recommend you use async.

https://github.com/caolan/async#filter

Example: fs.exists is an asynchronous function which checks for the existence of a file then calls a callback.

async.filter(['file1','file2','file3'], fs.exists, function(results){
    // results now equals an array of the existing files
});

Upvotes: 6

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