Microsoft Cognitive Services provides a number of APIs to take advantage of Machine Learning. One of the simplest APIs to use is Sentiment Analysis.

Sentiment Analysis examines one or more text entries and determines whether each text reflects a positive or negative sentiment. It returns a number between 0 and 1: A higher number indicates a more positive sentiment, while a lower number indicates a more negative sentiment.

To use this service, POST a JSON message to the following URL: https://westus.api.cognitive.microsoft.com/text/analytics/v2.0/sentiment

Unlike some web Cognitive Service URLs, this one takes no querystring parameters.

In the HTTP header, pass the following information: Content-Type and the Ocp-Apim-Subscription-Key.

The API is a simple REST web service located at https://api.projectoxford.ai/emotion/v1.0/recognize. POST to this service with a header that includes:
Ocp-Apim-Subscription-Key:xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx

where xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx is your key.

In the Content-Type, pass "application/json".

For the Ocp-Apim-Subscription-Key, include the the Text Analytics key. You can find your key at https://www.projectoxford.ai/Subscription?popup=True

In the body, pass a JSON object that contains an array of documents. Each document contains 3 properties:

language - the Language of the text you want to analyze. Valid values are "English", "Spanish", "French", and "Portuguese".

id - A string that uniquely identifies this document. Used to match the return value to the corresponding text.

text - the text to analyze

Below is a sample JSON body:

{
  "documents": [
    {
      "language": "English",
      "id": "text01",
      "text": "This is a great day."
    }
  ]
} 

After you POST this to the URL, you should expect a response that includes JSON. If all goes well, you will receive an HTTP 200 response and the returned JSON will include an array of documents (the same number that you passed in the Request body). Each Response document will contain

id - matching the id of the document in the Request document.

score - A value between 0 and 1. The higher the score, the more positive the sentiment of the text; The lower the score, the more negative the text sentiment.

You may also receive an array of errors. Each error contains the following properties:

id - matching the id of the document in the Request document.

message - a detailed error message.

Below is an sample response JSON body

{
  "documents": [
    {
      "score": 0.95412,
      "id": "text01"
    }
  ]
} 

Here is a bit of code to call this API from JavaScript. I am using jQuery's Ajax method and displaying output in a div, like the following:

<div id="OutputDiv">div> 

var subscriptionKey = "566375db01ad43dc8f62dcc8dc3e5c1f";
var textToAnalyze = "Life is beautiful"; 

var webSvcUrl = "https://westus.api.cognitive.microsoft.com/text/analytics/v2.0/sentiment";

var outputDiv = $("#OutputDiv");
outputDiv.text("Thinking..."); 

$.ajax({
    type: "POST",
    url: webSvcUrl,
    headers: { "Ocp-Apim-Subscription-Key": subscriptionKey },
    contentType: "application/json",
    data: '{"documents": [ { "language": "en", "id": "text01",  "text": "'+ textToAnalyze + '" }]}'
}).done(function (data) {
    if (data.errors.length > 0) {
        outputDiv.html("Error: " + data.errors[0]);
    }
    else if (data.documents.length > 0) {
        var score = data.documents[0].score;
        if (score > 0.5){
            outputText = "That is a Positive thing to say!";
        }
        else{
            outputText = "That is a Negative thing to say!";
            }
        outputDiv.html(outputText);
    }
    else {
        outputDiv.text("No text to analyze.");
    } 

}).fail(function (err) {
    $("#OutputDiv").text("ERROR! " + err.responseText);
});