197 lines
5.5 KiB
Markdown
197 lines
5.5 KiB
Markdown
---
|
|
id: 587d7fae367417b2b2512be3
|
|
title: Get JSON with the JavaScript XMLHttpRequest Method
|
|
challengeType: 6
|
|
forumTopicId: 301502
|
|
dashedName: 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. You'll learn how to update HTML with the data we get from APIs using a technology called AJAX.
|
|
|
|
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 freeCodeCamp's Cat Photo API. Here's the code you can put in your click event to do this:
|
|
|
|
```js
|
|
const req = new XMLHttpRequest();
|
|
req.open("GET",'/json/cats.json',true);
|
|
req.send();
|
|
req.onload = function(){
|
|
const 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 freeCodeCamp 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.
|
|
|
|
# --hints--
|
|
|
|
Your code should create a new `XMLHttpRequest`.
|
|
|
|
```js
|
|
assert(code.match(/new\s+?XMLHttpRequest\(\s*?\)/g));
|
|
```
|
|
|
|
Your code should use the `open` method to initialize a `GET` request to the freeCodeCamp Cat Photo API.
|
|
|
|
```js
|
|
assert(
|
|
code.match(
|
|
/\.open\(\s*?('|")GET\1\s*?,\s*?('|")\/json\/cats\.json\2\s*?,\s*?true\s*?\)/g
|
|
)
|
|
);
|
|
```
|
|
|
|
Your code should use the `send` method to send the request.
|
|
|
|
```js
|
|
assert(code.match(/\.send\(\s*\)/g));
|
|
```
|
|
|
|
Your code should have an `onload` event handler set to a function.
|
|
|
|
```js
|
|
assert(
|
|
code.match(/\.onload\s*=\s*(function|\(\s*?\))\s*?(\(\s*?\)|\=\>)\s*?{/g)
|
|
);
|
|
```
|
|
|
|
Your code should use the `JSON.parse` method to parse the `responseText`.
|
|
|
|
```js
|
|
assert(code.match(/JSON\s*\.parse\(\s*.*\.responseText\s*\)/g));
|
|
```
|
|
|
|
Your code should get the element with class `message` and change its inner HTML to the string of JSON data.
|
|
|
|
```js
|
|
assert(
|
|
code.match(
|
|
/document\s*\.getElementsByClassName\(\s*?('|")message\1\s*?\)\[0\]\s*\.innerHTML\s*?=\s*?JSON\.stringify\(.+?\)/g
|
|
)
|
|
);
|
|
```
|
|
|
|
# --seed--
|
|
|
|
## --seed-contents--
|
|
|
|
```html
|
|
<script>
|
|
document.addEventListener('DOMContentLoaded', function(){
|
|
document.getElementById('getMessage').onclick = function(){
|
|
// Add your code below this line
|
|
|
|
|
|
// Add your code above this line
|
|
};
|
|
});
|
|
</script>
|
|
|
|
<style>
|
|
body {
|
|
text-align: center;
|
|
font-family: "Helvetica", sans-serif;
|
|
}
|
|
h1 {
|
|
font-size: 2em;
|
|
font-weight: bold;
|
|
}
|
|
.box {
|
|
border-radius: 5px;
|
|
background-color: #eee;
|
|
padding: 20px 5px;
|
|
}
|
|
button {
|
|
color: white;
|
|
background-color: #4791d0;
|
|
border-radius: 5px;
|
|
border: 1px solid #4791d0;
|
|
padding: 5px 10px 8px 10px;
|
|
}
|
|
button:hover {
|
|
background-color: #0F5897;
|
|
border: 1px solid #0F5897;
|
|
}
|
|
</style>
|
|
|
|
<h1>Cat Photo Finder</h1>
|
|
<p class="message box">
|
|
The message will go here
|
|
</p>
|
|
<p>
|
|
<button id="getMessage">
|
|
Get Message
|
|
</button>
|
|
</p>
|
|
```
|
|
|
|
# --solutions--
|
|
|
|
```html
|
|
<script>
|
|
document.addEventListener('DOMContentLoaded',function(){
|
|
document.getElementById('getMessage').onclick = function(){
|
|
const req = new XMLHttpRequest();
|
|
req.open('GET', '/json/cats.json', true);
|
|
req.send();
|
|
req.onload = () => {
|
|
const json = JSON.parse(req.responseText);
|
|
document.getElementsByClassName('message')[0].innerHTML = JSON.stringify(json);
|
|
};
|
|
};
|
|
});
|
|
</script>
|
|
|
|
<style>
|
|
body {
|
|
text-align: center;
|
|
font-family: "Helvetica", sans-serif;
|
|
}
|
|
h1 {
|
|
font-size: 2em;
|
|
font-weight: bold;
|
|
}
|
|
.box {
|
|
border-radius: 5px;
|
|
background-color: #eee;
|
|
padding: 20px 5px;
|
|
}
|
|
button {
|
|
color: white;
|
|
background-color: #4791d0;
|
|
border-radius: 5px;
|
|
border: 1px solid #4791d0;
|
|
padding: 5px 10px 8px 10px;
|
|
}
|
|
button:hover {
|
|
background-color: #0F5897;
|
|
border: 1px solid #0F5897;
|
|
}
|
|
</style>
|
|
|
|
<h1>Cat Photo Finder</h1>
|
|
<p class="message box">
|
|
The message will go here
|
|
</p>
|
|
<p>
|
|
<button id="getMessage">
|
|
Get Message
|
|
</button>
|
|
</p>
|
|
```
|