I am new to Express, and having trouble sending data from backend to front end. Here is what I want to do: I have a Google Map API on the homepage (home.ejs). app.js is the server code: when the page is loaded, app.js generate some random locations and send to home.ejs, so home.ejs use those locations as Markers. Now I want to add event listeners to each of these markers, so that when mouse is over it, it send a GET request to server, and request a picture to display.
I feel it a big challenge for me to send the request/data back and forth. When the mouse is over, the home.ejs sends a GET Request to /getImge/:num route, and app.js responds to that request by retrieving the image url, and redirect to "/" and sends the url to it. This is where I get the "Can't set headers after they are sent".
I am so new to Express and ejs that I don't even know if I am on the right track. How should I implement this to get the communication through?
This is the app.js server file
var express = require("express");
var app = express();
//app.use(express.static(__dirname + "/public"));
app.use(express.static(__dirname));
app.set("view engine","ejs");
var lng_min = -84.161;
var lng_max = -83.688;
var lat_min = 35.849;
var lat_max = 36.067;
var urls = [
"http://cdn1-www.dogtime.com/assets/uploads/2015/01/file_21032_the-most-popular-dog-and-cat-names.jpg",
"http://qltyctrl.com/wp-content/uploads/2014/03/Sad-Dog-and-Cat.jpg",
"https://blog-photos.dogvacay.com/blog/wp-content/uploads/2015/07/dog-cat-smarter-ftr.jpg",
"http://qltyctrl.com/wp-content/uploads/2014/03/Dog-and-Cat-on-a-Log.jpg",
"http://images.boomsbeat.com/data/images/full/31730/cat-and-dog_1-jpg.jpg",
"http://www.vetlocator.com/dailypaws/wp-content/uploads/2012/04/dog-cat2.jpg",
"http://qltyctrl.com/wp-content/uploads/2014/03/Old-Dog-and-Cat-Sleepy-Embrace.jpg",
"https://encrypted-tbn0.gstatic.com/images?q=tbn:ANd9GcQXNMdvNfc3WYMqbPrJrnjgHJRp2zB1y9vx545LfO-_U5_yvgBo",
"http://www.vetlocator.com/dailypaws/wp-content/uploads/2012/04/dog-cat8.jpg",
"http://www.maddiesfund.org/assets/metaImage/robust-dog-cat-foster.jpg"
]
var numLocations = 10;
var data = [];
function generateData() {
// generate random locations and the url to download pictures
for (var i = 0; i < numLocations; ++i) {
var lng = Math.random() * (lng_max - lng_min) + lng_min;
var lat = Math.random() * (lat_max - lat_min) + lat_min;
var tuple = {
id: i,
lng: lng,
lat: lat,
pic: urls[i]
};
data.push(tuple);
}
}
app.get("/", function(req, res) {
//res.send("Hello it works");
data = [];
generateData();
res.render("home.ejs", {data: data});
});
app.get("/getImg/:num", function(req, res) {
console.log(req.params.num);
var i = Number(req.params.num);
res.redirect("/");
res.send({imgUrl: data[i].pic});
});
app.listen(process.env.PORT, process.env.IP, function() {
console.log("Server Started!");
});
home.ejs file:
<!DOCTYPE html>
<html>
<head>
<title>Demo</title>
<link rel="stylesheet" type="text/css" href="/public/app.css">
</head>
<body>
<div id="map">
</div>
<script>
var data = <%- JSON.stringify(data) %>;
console.log(data.length);
function initMap() {
var loc = {lat: 35.9606, lng: -83.9207};
var map = new google.maps.Map(document.getElementById('map'), {
zoom: 10,
center: loc
});
for (var i = 0; i < data.length; ++i) {
var loc = {lat: data[i].lat, lng: data[i].lng};
var marker = new google.maps.Marker({
position: loc,
map: map
// id: i
});
var infowindow = new google.maps.InfoWindow();
google.maps.event.addListener(marker, 'mouseover', (function(marker) {
return function() {
// var content = '<div id="imgDisplay">'
// + '<img src="http://www.maddiesfund.org/assets/metaImage/robust-dog-cat-foster.jpg">'
// + '</div>';
// infowindow.setContent(content);
// infowindow.open(map, marker);
var xhr = new XMLHttpRequest();
var params = 3;
xhr.open('GET','/getImg/'+params, true);
xhr.onreadystatechange = function() {
if (xhr.readyState == 4 && xhr.status == 200) {
console.log(responseText);
}
}
//xhr.send(params);
xhr.send();
}
})(marker));
}
}
</script>
<script async defer
src="https://maps.googleapis.com/maps/api/js?key=AIzaSyAOwfkV_GbUXyH2s8iD0gS6pje9J3R96dM&callback=initMap">
</script>
</body>
</html>
via daydayup
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