Web API

Great data is an essential part of many apps built today and the Web API component enables apps to retrieve data from any public or private API (application programming interface) service on the web. For more advanced developers who have write access to a private API, this component also enables you to upload and delete data.

To see what public APIs are available, we recommend this list from Todd Mottoโ€‹

For most public APIs, you'll likely have to first create an account to get your own unique API key. This is usually to prevent individuals from making too many requests or to charge developers when they exceed certain free limits.

Properties

Once you have the API key, you'll need to enter the unique URL into the property field of the Web API component

Property

Description

Required?

URL

The url for the web request which usually contains an API key

Required

Query Parameter

Specifies some parameters of the data

Optional

Body

Body of your API call

Optional

Headers

Specifies some meta-data, eg: usernames and passwords

Optional

Setting Query Parameters and Headers

Query parameters and headers can be set in the designer or in the blocks editor. In the example below you can add any property:value pair you want. You can add as many params to your app as you need, but each parameter has to be added one at a time.

In the blocks editor, it is possible to use the create object block to add multiple property:value pairs simultaneously.

You can learn more about creating objects in the Objects blocks.

Get and Format (parse) Data

To retrieve data from an API, you simply need to use the Get block.

Event

Description

Get (response, status,error)

Performs an HTTP GET request using the Url property and retrieves the response. Reports status of request and if request does not go through, will report an error

Most APIs will return data in JSON format, so we'll take a few moments to walk through a few examples of how to parse this data using our Object blocks

Get Simple Properties

Example 1: Open Weather Map APIโ€‹

You can find a working example of this in the sample app, Office Weather & Traffic.

One of the most common output formats for APIs is JSON, short for Javascript Object Notation. The Open Weather Map API returns a JSON file like the one below.

{
"coord":{"lon":85.17,"lat":26.67},
"weather":[{"id":804,"main":"Clouds","description":"overcast clouds","icon":"04n"}],
"base":"stations",
"main":{
"temp":298.312,
"pressure":1005.31,
"humidity":94,
"temp_min":298.312,
"temp_max":298.312,
"sea_level":1011.47,
"grnd_level":1005.31},
"wind":{"speed":2.96,"deg":79.5005},
"clouds":{"all":92},
"dt":1533157826,
"sys":{
"message":0.0034,
"country":"IN",
"sunrise":1533080664,
"sunset":1533128790},
"id":1273043,
"name":"Dhaka",
"cod":200
}

In your JSON response, objects can be found within the " quotes " followed by a colon :. The properties of the object is follows the colon : but is within the { curly brackets}.

In the example above, "base", "dt", "id", "name" and "cod" are simple properties of the JSON response. "coord" , "main" , "wind", "clouds" and "sys" are properties of the overall response, but each of these properties is also an object with properties of its own, or nested properties, contained within the { curly brackets }. "weather" is a one-item list which also contains an object.

Convert JSON to Object

The first step in parsing this response is converting the JSON response to an Object. Objects have properties (like name) that we can retrieve and display in our app. Objects can be embedded within another object.

Get Property of Object

Once you have converted the JSON into objects, you can then specify the objects and property that you are interested in. To get the name of the city we are viewing weather data for ("name": in line 22), we'll want to get the property name of the response:

Get Nested Properties

If we wanted to get the temperature in Dhaka from the Open Weather API above, we would need to do the following:

  • Convert the JSON response to an object

  • Get the property main of the response object

  • Get the property temp of main

We can write this as getting the property main.temp of the response object:

You can read about getting nested values from Objects here.

Get Properties from Lists

You can read about getting nested values and values from lists in Objects here. Let's work through an example.

You can find a working example of this in the sample app, Ride.

The JSON output of the Google Maps Distance Matrix API seems similar to the Open Weather Map API with one notable exception: it includes multi-item lists. Lists are items bounded by [ square brackets ].

{
"destination_addresses" : [ "Los Angeles, CA, USA" ],
"origin_addresses" : [ "San Francisco, CA, USA" ],
"rows" : [
{
"elements" : [
{
"distance" : {
"text" : "617 km",
"value" : 616620
},
"duration" : {
"text" : "5 hours 45 mins",
"value" : 20680
},
"status" : "OK"
}
]
}
],
"status" : "OK"
}

If you want to retrieve the "text" property in line 13, you'll have to:

  • convert the JSON to an object

  • select the "rows" property of the object

  • select the first item in the list

  • select the "elements" property of the rows object

  • select the first item in the list

  • select the "duration" property of the elements object

  • select the "text" property of the duration object

You can see the example below for how this would look using the Object and List blocks

This can also be written as the property rows[1].elements[1].duration.text of the response:

Upload data

Uploading and deleting data is usually reserved for a private API that you or your organization owns

Event

Description

Put (response, status,error)

Performs an HTTP PUT request using the Url property and retrieves the response. Reports status of request and if request does not go through, will report an error

Post (response, status,error)

Performs an HTTP POST request using the Url property and retrieves the response. Reports status of request and if request does not go through, will report an error

Patch (response, status, error)

Performs an HTTP PATCH request using the Url property and retrieves the response. Reports status of request and if request does not go through, will report an error

Delete data

Event

Description

Delete (response, status,error)

Performs an HTTP DELETE request using the Url property and retrieves the response. Reports status of request and if request does not go through, will report an error

See Also

You can also post and receive messages between a web page and a Web Viewer using the Post Message function. Read more about that here.