How to load JSON data on Node.js
Question
I am working to load JSON data using Node/express.js and plot it on map. As first start, I am inspired by the example presented in the repp leaflet-geojson-stream. https://github.com/tmcw/leaflet-geojson-stream/tree/master/example
Client: https://github.com/tmcw/leaflet-geojson-stream/blob/master/example/client.js
var L = require('leaflet'),
leafletStream = require('../');
L.Icon.Default.imagePath = 'http://leafletjs.com/dist/images';
window.onload = function() {
var div = document.body.appendChild(document.createElement('div'));
div.style.cssText = 'height:500px;';
var map = L.map(div).setView([0, 0], 2);
L.tileLayer('http://a.tile.openstreetmap.org/{z}/{x}/{y}.png').addTo(map);
var gj = L.geoJson().addTo(map);
leafletStream.ajax('/points.geojson', gj)
.on('end', function() {
});
};
Server : https://github.com/tmcw/leaflet-geojson-stream/blob/master/example/server.js
var express = require('express'),
browserify = require('browserify'),
app = express();
app.get('/', function(req, res) {
res.send('<html><head><link rel="stylesheet" href="http://cdn.leafletjs.com/leaflet-0.6.4/leaflet.css" /></head><body><script src="bundle.js"></script></html>');
});
app.get('/bundle.js', function(req, res) {
var b = browserify();
b.add('./client.js');
b.bundle().pipe(res);
});
app.get('/points.geojson', function(req, res) {
res.write('{"type":"FeatureCollection","features":[');
var i = 0, die = 0;
function send() {
if (++i > 20) {
res.write(JSON.stringify(randomFeature()) + '\n,\n');
i = 0;
} else {
// it seems like writing newlines here causes the buffer to
// flush
res.write('\n');
}
if (die++ > 1000) {
res.write(JSON.stringify(randomFeature()));
res.write(']');
res.end();
return;
}
setTimeout(send, 10);
}
send();
});
app.listen(3000);
function randomFeature() {
return {
type: 'Feature',
geometry: {
type: 'Point',
coordinates: [
(Math.random() - 0.5) * 360,
(Math.random() - 0.5) * 180
]
},
properties: {}
};
}
In the project, they create random json file. I wanted to read json file, then plot it. The reason I want to "Stream data" is to deal with the size of file (I know that there is better and easier ways to load json data), But I wanted to use this module.
I modified the server script :
var express = require('express'),
browserify = require('browserify'),
app = express();
app.get('/', function(req, res) {
res.send('<html><head><link rel="stylesheet" href="http://cdn.leafletjs.com/leaflet-0.6.4/leaflet.css" /></head><body><script src="bundle.js"></script></html>');
});
app.get('/bundle.js', function(req, res) {
var b = browserify();
b.add('./client.js');
b.bundle().pipe(res);
});
var o = require('../output_.geojson');
app.get('/points.geojson', function(req, res) {
res.json(o);
});
app.listen(3000);
res.write('');
But I am getting error :
/Users/macbook/leaflet-geojson-stream/output_.geojson:1
(function (exports, require, module, __filename, __dirname) { "type":"FeatureC
^
SyntaxError: Unexpected token :
at Module._compile (module.js:439:25)
at Object.Module._extensions..js (module.js:474:10)
at Module.load (module.js:356:32)
at Function.Module._load (module.js:312:12)
at Module.require (module.js:364:17)
at require (module.js:380:17)
at Object.<anonymous> (/Users/macbook/leaflet-geojson-stream/example/server.js:15:9)
at Module._compile (module.js:456:26)
at Object.Module._extensions..js (module.js:474:10)
at Module.load (module.js:356:32)
Can anyone give a hint on what should I do in order to read and load json external file to plot the data.
2 answers
solution1
2 2014-03-31 12:53:20
The : isn't expected, because you're in a function at that point.
To parse JSON, you simply have to call JSON.parse() , as stated in How to parse JSON using Node.js? . So you read the file, get the JSON String that's in there, and put it through JSON.parse()
solution2
1 2014-03-31 15:10:13
You are currently loading the whole JSON file into memory by 'requiring' it.
Instead you want to stream the file because it is big and so use the fs.createReadStream function:
var fs = require('fs');
app.get('/points.geojson', function(req, res) {
res.setHeader('Content-Type', 'application/json');
fs.createReadStream(__dirname + '../output_.geojson').pipe(res);
});
Also make sure that the contents of ../output_.geojson is actually valid JSON. You can use JSONLint to check - the file should with '{' or '[' and NOT have Javascript functions inside.
The technical post webpages of this site follow the CC BY-SA 4.0 protocol. If you need to reprint, please indicate the site URL or the original address.Any question please contact:yoyou2525@163.com.