How to pass additional parameter to jquery $.(post) callback function?

Question

I am writing this code where I am sending a sequence of asynchronous post requests by using a loop. When the callback related with the post request is called I want to use the loop variable which I directly cannot use because of javascript scoping rules. The code is like this:

for(i=0;i<10;i++)
{
$.post(url,requestData,function(data,status,xhr){
// use variable i
}

I cannot directly use i due to scoping rules related to callbacks in javascript. So I want to pass 'i' as a parameter to the callback but the documentation says there can be only 3 parameters associated with this callback. Is there any way to pass additional parameter?

Yousaf · Accepted Answer · 2020-05-30 07:36:46Z

2

You can use the variable i inside the callback if i is block scoped. Declare i with let keyword

for(let i=0;i<10;i++)
{
   $.post(url,requestData,function(data,status,xhr){
      // use variable i
   }
}

Here's a demo

const $ = {
  post: function(callback) {
    setTimeout(() => callback(123, 'OK', null), 1000);
  }
}

for(let i=0;i<5;i++)
{
     $.post(function(data,status,xhr) {
         // use variable i
       console.log(i);
     })
}

answered May 30, 2020 at 7:36

Yousaf

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Comments

Chase · Accepted Answer · 2020-05-30 07:36:25Z

0

I am using setTimeout here to demonstrate an async task (such as your $.post event).

for (i=0; i<10; i++) {
  setTimeout(() => {
    console.log(i);
  }, 1000);
}

i has changed before you get to run your console.log.

Instead, you must retain a COPY of the i value at the appropriate number.

for (i=0; i<10; i++) {
  const idx = i;
  setTimeout(() => {
    console.log(idx);
  }, 1000);
}

answered May 30, 2020 at 7:36

Chase

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