how to make for loop in async.parallel in node.js

Question

I have a code snippet like the following.

async.parallel({

    foo: function(call) {

      request.get('...?node=foo', function (error, response, body) {

        var last=JSON.parse(body);
        call(null,last.data.result);
      });

    },
    bar: function(call) {
      request.get('...node=bar', function (error, response, body) {

        var last=JSON.parse(body);
        call(null,last.data.result);
      });
    }
  }, function(err, results) {
    callback(results)
  });

but I want to that in loop...that is to say,like the following.

var node = ['foo', 'bar'];
async.parallel({

  for (var i = 0; i < node.length; i++) {
    node[i]: function(call) {

      request.get('...?node=' + node[i] + '', function(error, response, body) {

        var last = JSON.parse(body);
        call(null, last.data.result);
      });

    }
  }

}, function(err, results) {
  callback(results)
});

it does not work...how to make it? can you help me?

async.map()

Patrick Roberts
– Patrick Roberts

2017-07-24 13:41:18 +00:00
Commented Jul 24, 2017 at 13:41 — Patrick Roberts
– Patrick Roberts, Commented Jul 24, 2017 at 13:41

Community · Accepted Answer · 2020-06-20 09:12:55Z

You have one of two options. One is to read the documentation for async.map(), which would be the more canonical approach using async.

That would look something like this:

async.map(['foo', 'bar'], function (node, callback) {
  request.get('...?node=' + encodeURIComponent(node), function (error, response, body) {
    if (error) return callback(error)
    var last = JSON.parse(body)
    callback(null, last.data.results)
  })
}, function (error, results) {
  // handle error
  callback(results)
})

Your second option would be to use Promise.all() with a synchronous Array#map(), removing the dependency for async entirely, though you'll probably want a polyfill like bluebird until Promises are used in more substantial percentage of browsers.

Here's how you'd implement the latter solution using native Promises:

Promise.all(['foo', 'bar'].map(function (node) {
  return new Promise(function (resolve, reject) {
    request.get('...?node=' + encodeURIComponent(node), function (error, response, body) {
      if (error) return reject(error)
      var last = JSON.parse(body)
      resolve(last.data.result)
    })
  })
})).then(function (results) {
  callback(results)
}).catch(function (error) {
  // handle error
})

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