{ "name": "JSON APIs and Ajax", "order": 2, "time": "2 hours", "helpRoom": "Help", "required": [ { "link": "https://cdnjs.cloudflare.com/ajax/libs/twitter-bootstrap/3.3.7/css/bootstrap.css" } ], "challenges": [ { "id": "587d7fad367417b2b2512be0", "title": "Introduction to the JSON APIs and Ajax Challenges", "description": [ [ "http://imgs.xkcd.com/comics/api.png", "XKCD web comic with a user sitting at a computer reading the instructions for an API Guide for a site. The text below notes \"If you do things right, it can take people awhile to realize that your 'API documentation' is just instructions for how to look at your website.\"", "Similar to how User Interfaces help people use programs, Application Programming Interfaces (APIs) help programs interact with other programs. APIs are tools that computers use to communicate with one another, in part to send and receive data. You can use API functionality in your page once you understand how to make requests and process data from it. Programmers often use Ajax technologies when working with APIs.

The term Ajax originated as an acronym for Asynchronous JavaScript And XML. It refers to a group of technologies that make asynchronous requests to a server to transfer data, then load any returned data into the page. An asynchronous process has a couple key properties. The browser does not stop loading a page to wait for the server's response. Also, the browser inserts updated data into part of the page without having to refresh the entire page.

User experience benefits from asynchronous processes in several ways. Pages load faster since the browser isn't waiting for the server to respond in the middle of a page render. Requests and transfers happen in the background, without interrupting what the user is doing. When the browser receives new data, only the necessary area of the page refreshes. These qualities especially enhance the user experience for single page applications.

The data transferred between the browser and server is often in a format called JavaScript Object Notation (JSON). JSON resembles JavaScript object literal syntax, except that it's transferred as a string. Once received, it can be converted into an object and used in a script.

This section covers how to transfer and use data using Ajax technologies with a Free Code Camp API.", "" ] ], "releasedOn": "", "challengeSeed": [], "tests": [], "type": "Waypoint", "challengeType": 7, "isRequired": false, "titleEs": "", "descriptionEs": [ [] ], "titleFr": "", "descriptionFr": [ [] ], "titleDe": "", "descriptionDe": [ [] ] }, { "id": "587d7fad367417b2b2512be1", "title": "Trigger Click Events with JavaScript", "description": [ "This section covers how to get data from APIs. APIs - or Application Programming Interfaces - are tools that computers use to communicate with one another.", "You'll learn how to update HTML with the data we get from these APIs using a technology called Ajax.", "You want your code to execute only once your page has finished loading. For that purpose, you can attach a JavaScript event to the document called DOMContentLoaded. Here's the code that does this:", "
document.addEventListener('DOMContentLoaded',function() {

});
", "Next, you can implement a click event handler that goes inside of the DOMContentLoaded function by adding the following code:", "document.getElementById('getMessage').onclick=function(){};", "

Instructions

", "Add a click event handler inside of the DOMContentLoaded function for the element with id of getMessage." ], "challengeSeed": [ "", "", "

Cat Photo Finder

", "

", " The message will go here", "

", "

", " ", "

" ], "tests": [ "assert(code.match(/document\\.getElementById\\(\\s*?('|\")getMessage\\1\\s*?\\)/g), 'message: Your code should use the document.getElementById method to select the getMessage element.');", "assert(code.match(/\\.onclick=function\\(\\s*?\\)\\s*?{\\s*?};/g), 'message: Your code should add an onclick event handler.');" ], "solutions": [], "hints": [], "type": "waypoint", "challengeType": 0, "translations": { "de": { "description": [], "title": "" }, "fr": { "description": [], "title": "" }, "pt-br": { "description": [], "title": "" }, "ru": { "description": [], "title": "" } } }, { "id": "587d7fad367417b2b2512be2", "title": "Change Text with Click Events", "description": [ "When the click event happens, you can use JavaScript to update an HTML element.", "For example, when a user clicks the \"Get Message\" button, it changes the text of the element with the class message to say \"Here is the message\".", "This works by adding the following code within the click event:", "document.getElementsByClassName('message')[0].innerHTML=\"Here is the message\";", "

Instructions

", "Add code inside the onclick event handler to change the text inside the message element to say \"Here is the message\"." ], "challengeSeed": [ "", "", "

Cat Photo Finder

", "

", " The message will go here", "

", "

", " ", "

" ], "tests": [ "assert(code.match(/document\\.getElementsByClassName\\(\\s*?('|\")message\\1\\s*?\\)\\[0\\]\\.innerHTML\\s*?=\\s*?('|\")Here is the message\\2/g), 'message: Your code should use the document.getElementsByClassName method to select the element with class message and set its innerHTML to the given string.');" ], "solutions": [], "hints": [], "type": "waypoint", "challengeType": 0, "translations": { "de": { "description": [], "title": "" }, "fr": { "description": [], "title": "" }, "pt-br": { "description": [], "title": "" }, "ru": { "description": [], "title": "" } } }, { "id": "587d7fae367417b2b2512be3", "title": "Get JSON with the JavaScript XMLHttpRequest Method", "description": [ "You can also request data from an external source. This is where APIs come into play.", "Remember that APIs - or Application Programming Interfaces - are tools that computers use to communicate with one another.", "Most web APIs transfer data in a format called JSON. JSON stands for JavaScript Object Notation.", "JSON syntax looks very similar to JavaScript object literal notation. JSON has object properties and their current values, sandwiched between a { and a }.", "These properties and their values are often referred to as \"key-value pairs\".", "However, JSON transmitted by APIs are sent as bytes, and your application receives it as a string. These can be converted into JavaScript objects, but they are not JavaScript objects by default. The JSON.parse method parses the string and constructs the JavaScript object described by it.", "You can request the JSON from Free Code Camp's Cat Photo API. Here's the code you can put in your click event to do this:", "
req=new XMLHttpRequest();
req.open(\"GET\",'/json/cats.json',true);
req.send();
req.onload=function(){
json=JSON.parse(req.responseText);
document.getElementsByClassName('message')[0].innerHTML=JSON.stringify(json);
};
", "Here's a review of what each piece is doing. The JavaScript XMLHttpRequest object has a number of properties and methods that are used to transfer data. First, an instance of the XMLHttpRequest object is created and saved in the req variable.", "Next, the open method initializes a request - this example is requesting data from an API, therefore is a \"GET\" request. The second argument for open is the URL of the API you are requesting data from. The third argument is a Boolean value where true makes it an asynchronous request.", "The send method sends the request. Finally, the onload event handler parses the returned data and applies the JSON.stringify method to convert the JavaScript object into a string. This string is then inserted as the message text.", "

Instructions

", "Update the code to create and send a \"GET\" request to the Free Code Camp Cat Photo API. Then click the \"Get Message\" button. Your Ajax function will replace the \"The message will go here\" text with the raw JSON output from the API." ], "challengeSeed": [ "", "", "

Cat Photo Finder

", "

", " The message will go here", "

", "

", " ", "

" ], "tests": [ "assert(code.match(/new\\s+?XMLHttpRequest\\(\\s*?\\)/g), 'message: Your code should create a new XMLHttpRequest.');", "assert(code.match(/\\.open\\(\\s*?('|\")GET\\1\\s*?,\\s*?('|\")\\/json\\/cats\\.json\\2\\s*?,\\s*?true\\s*?\\)/g), 'message: Your code should use the open method to initialize a \"GET\" request to the Free Code Camp Cat Photo API.');", "assert(code.match(/\\.send\\(\\s*\\)/g), 'message: Your code should use the send method to send the request.');", "assert(code.match(/\\.onload=function\\(\\s*?\\)\\s*?{/g), 'message: Your code should have an onload event handler set to a function.');", "assert(code.match(/JSON\\.parse\\(.*\\.responseText\\)/g), 'message: Your code should use the JSON.parse method to parse the responseText.');", "assert(code.match(/document\\.getElementsByClassName\\(\\s*?('|\")message\\1\\s*?\\)\\[0\\]\\.innerHTML\\s*?=\\s*?JSON\\.stringify\\(.+?\\)/g), 'message: Your code should get the element with class message and change its inner HTML to the string of JSON data.');" ], "solutions": [ ], "hints": [], "type": "waypoint", "challengeType": 0, "translations": { "de": { "description": [], "title": "" }, "fr": { "description": [], "title": "" }, "pt-br": { "description": [], "title": "" }, "ru": { "description": [], "title": "" } } }, { "id": "587d7fae367417b2b2512be4", "title": "Access the JSON Data from an API", "description": [ "In the previous challenge, you saw how to get JSON data from the Free Code Camp Cat Photo API.", "Now you'll take a closer look at the returned data to better understand the JSON format. Recall some notation in JavaScript:", "
[ ] -> Square brackets represent an array
{ } -> Curly brackets represent an object
\" \" -> Double quotes represent a string. They are also used for key names in JSON
", "Understanding the structure of the data that an API returns is important because it influences how you retrieve the values you need.", "On the right, click the \"Get Message\" button to load the Free Code Camp Cat Photo API JSON into the HTML.", "The first and last character you see in the JSON data are square brackets [ ]. This means that the returned data is an array. The second character in the JSON data is a curly { bracket, which starts an object. Looking closely, you can see that there are three separate objects. The JSON data is an array of three objects, where each object contains information about a cat photo.", "You learned earlier that objects contain \"key-value pairs\" that are separated by commas. In the Cat Photo example, the first object has \"id\":0 where \"id\" is a key and 0 is its corresponding value. Similarly, there are keys for \"imageLink\", \"altText\", and \"codeNames\". Each cat photo object has these same keys, but with different values.", "Another interesting \"key-value pair\" in the first object is \"codeNames\":[\"Juggernaut\",\"Mrs. Wallace\",\"ButterCup\"]. Here \"codeNames\" is the key and its value is an array of three strings. It's possible to have arrays of objects as well as a key with an array as a value.", "Remember how to access data in arrays and objects. Arrays use bracket notation to access a specific index of an item. Objects use either bracket or dot notation to access the value of a given property. Here's an example that prints the \"altText\" of the first cat photo - note that the parsed JSON data in the editor is saved in a variable called json:", "
console.log(json[0].altText);
// Prints \"A white cat wearing a green helmet shaped melon on it's head.\"
", "

Instructions

", "For the cat with the \"id\" of 2, print to the console the second value in the codeNames array. You should use bracket and dot notation on the object (which is saved in the variable json) to access the value." ], "challengeSeed": [ "", "", "

Cat Photo Finder

", "

", " The message will go here", "

", "

", " ", "

" ], "tests": [ "assert(code.match(/(?:json\\[2\\]\\.codeNames\\[1\\]|json\\[2\\]\\[('|\")codeNames\\1\\]\\[1\\])/g), 'message: Your code should use bracket and dot notation to access the proper code name, and print \"Loki\" to the console.');" ], "solutions": [], "hints": [], "type": "waypoint", "challengeType": 0, "translations": { "de": { "description": [], "title": "" }, "fr": { "description": [], "title": "" }, "pt-br": { "description": [], "title": "" }, "ru": { "description": [], "title": "" } } }, { "id": "587d7fae367417b2b2512be5", "title": "Convert JSON Data to HTML", "description": [ "Now that you're getting data from a JSON API, you can display it in the HTML.", "You can use a forEach method to loop through the data since the cat photo objects are held in an array. As you get to each item, you can modify the HTML elements.", "First, declare an html variable with var html = \"\";.", "Then, loop through the JSON, adding HTML to the variable that wraps the key names in strong tags, followed by the value. When the loop is finished, you render it.", "Here's the code that does this:", "
json.forEach(function(val) {
var keys = Object.keys(val);
html += \"<div class = 'cat'>\";
keys.forEach(function(key) {
html += \"<strong>\" + key + \"</strong>: \" + val[key] + \"<br>\";
});
html += \"</div><br>\";
});
", "

Instructions

", "Add a forEach method to loop over the JSON data and create the HTML elements to display it." ], "challengeSeed": [ "", "", "

Cat Photo Finder

", "

", " The message will go here", "

", "

", " ", "

" ], "tests": [ "assert(code.match(/json\\.forEach/g), 'message: Your code should use a forEach method to loop over the JSON data from the API.');" ], "solutions": [], "hints": [], "type": "waypoint", "challengeType": 0, "translations": { "de": { "description": [], "title": "" }, "fr": { "description": [], "title": "" }, "pt-br": { "description": [], "title": "" }, "ru": { "description": [], "title": "" } } }, { "id": "587d7fae367417b2b2512be6", "title": "Render Images from Data Sources", "description": [ "The last few challenges showed that each object in the JSON array contains an imageLink key with a value that is the URL of a cat's image.", "When you're looping through these objects, you can use this imageLink property to display this image in an img element.", "Here's the code that does this:", "html += \"<img src = '\" + val.imageLink + \"' \" + \"alt='\" + val.altText + \"'>\";", "

Instructions

", "Add code to use the imageLink and altText properties in an img tag." ], "challengeSeed": [ "", "", "

Cat Photo Finder

", "

", " The message will go here", "

", "

", " ", "

" ], "tests": [ "assert(code.match(/val\\.imageLink/g), 'message: You should use the imageLink property to display the images.');" ], "solutions": [], "hints": [], "type": "waypoint", "challengeType": 0, "translations": { "de": { "description": [], "title": "" }, "fr": { "description": [], "title": "" }, "pt-br": { "description": [], "title": "" }, "ru": { "description": [], "title": "" } } }, { "id": "587d7fae367417b2b2512be7", "title": "Pre-filter JSON", "description": [ "If you don't want to render every cat photo you get from the Free Code Camp Cat Photo API, you can pre-filter the JSON before looping through it.", "Given that the JSON data is stored in an array, you can use the filter method to filter out the cat whose \"id\" key has a value of 1.", "Here's the code to do this:", "
json = json.filter(function(val) {
return (val.id !== 1);
});
", "

Instructions

", "Add code to filter the json data to remove the cat with the \"id\" value of 1." ], "challengeSeed": [ "", "", "

Cat Photo Finder

", "

", " The message will go here", "

", "

", " ", "

" ], "tests": [ "assert(code.match(/json\\.filter/g), 'message: Your code should use the filter method.');" ], "solutions": [], "hints": [], "type": "waypoint", "challengeType": 0, "translations": { "de": { "description": [], "title": "" }, "fr": { "description": [], "title": "" }, "pt-br": { "description": [], "title": "" }, "ru": { "description": [], "title": "" } } }, { "id": "587d7faf367417b2b2512be8", "title": "Get Geolocation Data", "description": [ "Another cool thing you can do is access your user's current location. Every browser has a built in navigator that can give you this information.", "The navigator will get the user's current longitude and latitude.", "You will see a prompt to allow or block this site from knowing your current location. The challenge can be completed either way, as long as the code is correct.", "By selecting allow, you will see the text on the output phone change to your latitude and longitude.", "Here's code that does this:", "
if (navigator.geolocation){
navigator.geolocation.getCurrentPosition(function(position) {
document.getElementById('data').innerHTML=\"latitude: \"+ position.coords.latitude + \"<br>longitude: \" + position.coords.longitude;
});
}
", "First, it checks if the navigator.geolocation object exists. If it does, the getCurrentPosition method on that object is called, which initiates an asynchronous request for the user's position. If the request is successful, the callback function in the method runs. This function accesses the position object's values for latitude and longitude using dot notation and updates the HTML.", "

Instructions

", "Add the example code inside the script tags to check a user's current location and insert it into the HTML." ], "challengeSeed": [ "", "

You are here:

", "
", "", "
" ], "tests": [ "assert(code.match(/navigator\\.geolocation\\.getCurrentPosition/g), 'message: Your code should use navigator.geolocation to access the user's current location.');", "assert(code.match(/position\\.coords\\.latitude/g), 'message: Your code should use position.coords.latitude to display the user's latitudinal location.');", "assert(code.match(/position\\.coords\\.longitude/g), 'message: Your code should use position.coords.longitude to display the user's longitudinal location.');", "assert(code.match(/document\\.getElementById\\(\\s*?('|\")data\\1\\s*?\\)\\.innerHTML/g), 'message: You should display the user's position within the data div element.');" ], "solutions": [], "hints": [], "type": "waypoint", "challengeType": 0, "translations": { "de": { "description": [], "title": "" }, "fr": { "description": [], "title": "" }, "pt-br": { "description": [], "title": "" }, "ru": { "description": [], "title": "" } } }, { "id": "587d7faf367417b2b2512be9", "title": "Post Data with the JavaScript XMLHttpRequest Method", "description": [ "In the previous examples, you received data from an external resource. You can also send data to an external resource, as long as that resource supports Ajax requests and you know the URL.", "JavaScript's XMLHttpRequest method is also used to post data to a server. Here's an example:", "
req=new XMLHttpRequest();
req.open(\"POST\",url,true);
req.setRequestHeader('Content-Type','text/plain');
req.onreadystatechange=function(){
if(req.readyState==4 && req.status==200){
document.getElementsByClassName('message')[0].innerHTML=req.responseText;
}
};
req.send(userName);
", "You've seen several of these methods before. Here the open method initializes the request as a \"POST\" to the given URL of the external resource, and uses the true Boolean to make it asynchronous.", "The setRequestHeader method sets the value of an HTTP request header, which contains information about the sender and the request. It must be called after the open method, but before the send method. The two parameters are the name of the header and the value to set as the body of that header.", "Next, the onreadystatechange event listener handles a change in the state of the request. A readyState of 4 means the operation is complete, and a status of 200 means it was a successful request. The document's HTML can be updated.", "Finally, the send method sends the request with the userName value, which was given by the user in the input field.", "

Instructions

", "Update the code to create and send a \"POST\" request. Then enter your name in input box and click \"Send Message\". Your Ajax function will replace \"Reply from Server will be here.\" with the reply of the server. In this case, it is your name appended with \" loves cats\"." ], "challengeSeed": [ "", "", "

Cat Friends

", "

", " Reply from Server will be here", "

", "

", " ", " ", "

" ], "tests": [ "assert(code.match(/new\\s+?XMLHttpRequest\\(\\s*?\\)/g), 'message: Your code should create a new XMLHttpRequest.');", "assert(code.match(/\\.open\\(\\s*?('|\")POST\\1\\s*?,\\s*?url\\s*?,\\s*?true\\s*?\\)/g), 'message: Your code should use the open method to initialize a \"POST\" request to the server.');", "assert(code.match(/\\.setRequestHeader\\(\\s*?('|\")Content-Type\\1\\s*?,\\s*?('|\")text\\/plain\\2\\s*?\\)/g), 'message: Your code should use the setRequestHeader method.');", "assert(code.match(/\\.onreadystatechange\\s*?=/g), 'message: Your code should have an onreadystatechange event handler set to a function.');", "assert(code.match(/document\\.getElementsByClassName\\(\\s*?('|\")message\\1\\s*?\\)\\[0\\]\\.innerHTML\\s*?=\\s*?.+?\\.responseText/g), 'message: Your code should get the element with class message and change its inner HTML to the responseText.');", "assert(code.match(/\\.send\\(\\s*?userName\\s*?\\)/g), 'message: Your code should use the send method.');" ], "solutions": [], "hints": [], "type": "waypoint", "challengeType": 0, "translations": { "de": { "description": [], "title": "" }, "fr": { "description": [], "title": "" }, "pt-br": { "description": [], "title": "" }, "ru": { "description": [], "title": "" } } } ] }