Read specific character from file using JavaScript AJAX? - javascript

I need to find a way of reading data extracts from data files, where some of these files are quite large. The specific character place in the file is known and can be extracted using JavaScript code similar to that below (using JQuery).
The problem I am having is that my code reads the entire file into the buffer before processing, and for large files this is impractical. Is there a way that either code below can be altered or would perhaps a more efficient method be possible?
function startfn() {
var index = 1000;
$.ajax({
type: "GET",
url: "datafile.bin",
dataType: "text",
success: function(data) {procData(data,index);}
})
return 0;
}
function procData(strData, index) {
alert(strData.charCodeAt(index).toString(16)
+","+strData.charCodeAt(index+1).toString(16) +", "+
strData.charCodeAt(index+2).toString(16));
}

One way to do that is to use a backend service (Php for example) that do the extraction then just use ajax to get the result.

Related

Get JSON data from WFS/Geoserver

I am struggling with getting data from WFS in my GeoServer. I want to get specific properties from the JSON returned by WFS and use it in my html page filling a table. I have read lots of posts and documentation but I can't seem to make it work. I have:
(a) changed the web.inf file in my geoserver folder to enable jsonp
(b) tried combinations of outputFormat (json or text/javascript)
(c) tried different ways to parse the JSON (use . or [], JSON.parse or parseJSON etc),
(d) used JSON.stringify to test whether the ajax call works correctly (it does!!)
but, in the end, it always returns undefined!!
function wfs(longitude, latitude){
function getJson(data) {
var myVar1=data['avgtemp1'];
document.getElementById("v1").innerHTML = myVar;
}
var JsonUrl = "http://88.99.13.199:8080/geoserver/agristats/wfs?service=wfs&version=2.0.0&request=GetFeature&typeNames=agristats:beekeeping&cql_filter=INTERSECTS(geom,POINT(" + longitude + " " + latitude + "))&outputFormat=text/javascript&format_options=callback:getJson";
$.ajax({
type: 'GET',
url: JsonUrl,
dataType: 'jsonp',
jsonpCallback:'getJson',
success: getJson
});
}
wfs(38, 23);
Could you please help me?
You are close to it. First, you have a typo in the variable name you are writing (myVar1 vs myVar). Secondly, your function is receiving a Json object, so you must dive into its structure. First you get the features, then the 1st one, then the property array, then the property of your choice.
I suggest you read a tutorial on Json Objects, as you will surely want to loop through properties/items, validate they are not null etc.
function getJson(data) {
var myVar1=data.features[0].properties['avgtemp1'];
document.getElementById("v1").innerHTML = myVar1;
}
At last, don't forget to use the debugger in your favorite browser. put a breakpoint in your function and check the structure and content of data.

Ajax request, fetch JS array and make it available

I'm trying to fetch a JS array created by a PHP file and re-use the JS array in a JS script in the page. I have tried many different solutions found on this site but none seems to work but I don't know what the issue is with my script.
I have a PHP file that echoes the following:
[["content11", "content12", "content13", "content14","content15"],
["content21", "content22", "content23", "content24","content25"]]
I'm using a simple Ajax get to retrieve the data:
$.ajax({
type: "GET",
url: myUrlToPhpFile,
dataType: "html",
success : function(data)
{
result = data;
alert (result);
}
});
The alert displays the expected output from the PHP file but if I now try to access the array like result[0], it outputs "[" which is the first character. It looks like JS sees the output as a string rather than an array.
Is there something I should do to make JS understand it's a JS array?
I have seen many solution with JSON arrays but before going into this direction, I'd like to check if there are simple solutions with JS arrays (this would prevent me from rewriting too much code)
Thanks
Laurent
In you php file you need check that your arrays echos with json_encode.
echo json_encode($arr);
And in your javascript file:
$.ajax({
type: "GET",
url: myUrlToPhpFile,
dataType: "html", // json
success : function(data)
{
var res = JSON.parse(html);
alert(html); // show raw data
alert(res); // show parsed JSON
}
});
You can use JSON.parse to format the string back into an array.
JSON.parse(result)[0]
or
var result = JSON.parse(result);
result[0];
#Rho's answer should work fine, but it appears that you're using jQuery for your AJAX call, which gives you a shortcut; you can use $.getJSON instead of $.ajax, and it will read the data as JSON and provide you with the array immediately.
$.getJSON(myUrlToPhpFile, function(result) { ... });
This is really just a short way of writing what you already have, but with a dataType of json instead of html, so you could even do it that way if you prefer. This is all assuming that you're using jQuery of course, but your code was following their API so it seems a good bet that you're either using jQuery or something compatible.

How to display a json data from a existing url using ajax call

I Am new in working with json and jquery. I am trying to study the basics of json and jquery by working on some example. So I use existing json data in http://api.androidhive.info/contacts for my example. I want to display this data in my HTML page. My code is:
<html>
<head>
<title>jQuery Ajax Example with JSON Response</title>
<script src="//ajax.googleapis.com/ajax/libs/jquery/1.11.2/jquery.min.js" type="text/javascript"></script>
<script>
$(document).ready(function(){
$(':submit').on('click', function() { // This event fires when a button is clicked
alert("submitt worked.");
$.ajax({ // ajax call starts
url: 'http://api.androidhive.info/contacts/', // JQuery loads serverside.php
type: "GET",
dataType: 'json', // Choosing a JSON datatype
success: function (msg) {
alert("ajax worked.");
JsonpCallback(msg);
},
})
function JsonpCallback(json)
{
for (var i in json.contacts) {
$('#wines').append('contacts: ' + json.contacts[i] + '<br/>');
}
}
return false; // keeps the page from not refreshing
});
});
</script>
</head>
<body>
<form method="post" action="">
<button value="all" type="submit">Get!</button>
</form>
<div id="wines">
<!-- Javascript will print data in here when we have finished the page -->
</div>
</body>
</html>
can any one please give me some brief introduction to JSON and how it's working ?
Thanks in advance.
You are iterating the JSON wrong, in your case since you are using jQuery (as mentioned) you can use the $.each(json, callback); helper fron jQuery, you can see the documentation here Jquery $.each documentation
For an example implementation I've created this JSFIDDLE LINK
for you. Have a great day ahead. Don't forget that JSON means
Javascript Object Notation
It's an object.
$.each(jsonData.contacts, function(k, v)
{
console.log(v.name);
$('#name').append('<li>'+v.name+'</li>');
});
jQuery
Am try to study the basics of json and jquery
Is a Javascript library with lots of very usefull methods. If you want to create a dynamic website it is very recommended to look into jQuery. There are many site with great explanation on what jQuery can do. As far as your example is concerned: There is an issue when passing variables/data from one framework to another or even when simply storing data. Here comes JSON.
JSON
Or JavaScript Object Notation (JSON) is used to solve exactly that problem. What is basically does is take all the desired data (array, variable, object, string etc.) and writes it in a human readable and for other frameworks readable fashion. I use JSON to store data in files when no database is available or when passing data from one framework to another (like JS <-> PHP).
Your example code
What happens here:
$(':submit').on('click', function() { // This event fires when a button is clicked
alert("submitt worked."); // not yet
$.ajax({ // ajax call starts
url: 'http://api.androidhive.info/contacts/', // JQuery loads serverside.php --> this I don't know
type: "GET", // communication type
dataType: 'json', // Choosing a JSON datatype
success: function (msg) { // here, the whole content of the url is read, idealy it is in JSON format ofc
alert("ajax worked."); // hoorray
JsonpCallback(msg);
},
})
There is the serverside.php file that receives a GET command and returns HTML. All the HTML content is in JSON type (so no <stuff>, i.e. no actual HTML) and your success function returns that content in the msg variable. Typically you use something like
var obj = JSON.parse(text);
to convert the JSON data to Javascript variables. Read this here JSON in Javascript
JSONP
Now what if you want to do some domain crossing (as you suggested), then I strongly recommend to read this here What is JSONP all about? . It explains what JSONP is all about

Reading a CSV file with jQuery

I have a downloaded CSV file which I would like to parse and use to create JSON objects for each record. The file is on my local machine but I have read that JavaScript has security measures in place that prevent access to these files.
Some examples show using csv.js with the following:
$.ajax({
url: "G:\downloaded_files\filename.csv",
aync: false,
success: function (csvd) {
csv_as_array = $.csv.toArrays(csvd);
},
dataType: "text",
complete: function () {
// use the array of arrays (variable csv_as_array)
// for further processing
}
});
When running this it just creates a GET request in the console. I am treading on unfamiliar territory here so any explanations would be great.
If I was to do this using Ruby I would do this, which hopefully will give you an indication of what I am trying to achieve:
require 'csv'
class FileRead
csv_text = File.read('/home/richardlewis/Downloads/csvtest.csv')
csv = CSV.parse(csv_text, headers: true)
csv.each do |row|
hash = row.to_hash
puts(hash)
end
end
I'm hoping this makes sense and someone can point me in the right direction.
You cannot call local files (from hard dics) using Ajax, or by any means from a web browser. You will have to publish your file using some sort of server. If you are using Linux you should have an Apache server already installed.
You need a REST service that will return your file in some format. JSON is the best, because it's easy to manipulate JSON data on the front-end.
It would look like this:
$.ajax({
url: "http://localhost:8080/services/rest/get_file", // your rest address
...
});

Enumerating through Yahoo Pipes generated JSON with jQuery fails

I'm trying to lessen manual update work by using Yahoo Pipes and jQuery to update a table with upcoming events from a different domain. I have created this Pipe to gather the data, and it seems to work.
Now I am reading the JSON file with the following jQuery Script taken from this tutorial:
$.ajax({
type: "GET",
url: "http://pipes.yahoo.com/pipes/pipe.run?_id=57aa32bf3481c8dca0c07afcf9b9dc29&_render=json",
async: false,
beforeSend: function(x) {
if(x && x.overrideMimeType) {
x.overrideMimeType("application/j-son;charset=UTF-8");
}
},
dataType: "json",
success: function(data){
$('body').append(data.query.results.a.content);
}
});
The jQuery append failes, I guess because 'data.query.results.a.content' does not relate well to the JSON structure created by the pipe.
I've tried altering both the pipe and the append in several ways and am just short of giving up, I'd be very grateful for your Input.
Think you are parsing the json result incorrectly.
On viewing the json object here http://jsonviewer.stack.hu/
You will observe content node for each item is at value.items[0].a.content
i.e. try something like this :
$('body').append(data.value.items[0].a.content);
You will need to iterate the items array like this
$.each(data.value.items, function(index,element) {
$('body').append(element.a.content);
});
Try it on fiddle : http://jsfiddle.net/EFvJf/

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