CODEWITHSUNDEEP
node.jspromisesynchronization
Dev
Dev

Reputation: 423

nodejs synchronus call fast csv

I'm using fast csv for csv file read below is code given below

var csv = require("fast-csv");
csv.fromPath("userlists.csv")
.transform(function(obj){
    return {
        email: obj.email,
        firstname: obj.firstname,
        lastname: obj.lastname
    };
})       
.on("data", function(data){
   // Some promise call for API

})
.on("end", function(){
    response.send("Imported successfully");
    console.log("done");
});

Inside on("data", function(data){}) I'm calling some API using promise these API takes some time for processing. After reading csv file "Imported successfully" is showing immediately without waiting for API processed. I want to print Imported successfully at end of all API processing.

Upvotes: 1

Views: 2820

Answers (1)

Kishan Mundha
Kishan Mundha

Reputation: 3141

on("data", function(data){}) don't have full data. It call for every record. If we put api inside this, then this may call many time API.

on("end", function() {}) execute after csv import success. It's not depend on any api, It's dependency only csv import.

We have two approach to do this.

1. Call API in end method

store data in array and finally call in on("end", function() {}) method.

var csvdata = [];

var csv = require("fast-csv");
csv.fromPath("userlists.csv")
.transform(function(obj){
    return obj;
})       
.on("data", function(data){
   csvdata.push(data);
})
.on("end", function(){
    // Some promise call for API

    // In API promise callback
    response.send("Imported successfully");
    console.log("done");
});

2. Create callback function

If first approach not suitable for condition then we can use this approach. but first approach is more better.

In this approach we create a callback function which we call in api callback. As we know api call multiple time in this approach, because this on("data" method call for every record. so we need to call after all api success.

var csv = require("fast-csv");
csv.fromPath("userlists.csv")
.transform(function(obj){
    return {
        email: obj.email,
        firstname: obj.firstname,
        lastname: obj.lastname
    };
})       
.on("data", function(data){
   // Some promise call for API

   // promises callback handle
   Promise.all([/*api promise list here*/]).then(function() {
       handleSuccessResponse(response);
   }
})
.on("end", function(){
});

function handleSuccessResponse(response) {
    response.send("Imported successfully");
    console.log("done");
}

Upvotes: 1

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