Function Composition in JavaScript with Array.prototype.reduceRight

Functional programming in JavaScript has rocketed in popularity over the last few years. While a handful of its regularly-promoted tenets, such as immutability, require runtime workarounds, the language’s first-class treatment of functions has proven its support of composable code driven by this fundamental primitive. Before covering how one can dynamically compose functions from other functions, let’s take a brief step back.

Functional programming in JavaScript has rocketed in popularity over the last few years. While a handful of its regularly-promoted tenets, such as immutability, require runtime workarounds, the language’s first-class treatment of functions has proven its support of composable code driven by this fundamental primitive. Before covering how one can dynamically compose functions from other functions, let’s take a brief step back.


What is a Function?

Effectively, a function is a procedure that allows one to perform a set of imperative steps to either perform side effects or to return a value. For example:

function getFullName(person) {
  return `${person.firstName} ${person.surname}`;
}

When this function is invoked with an object possessing firstName and lastName properties, getFullName will return a string containing the two corresponding values:

const character = {
  firstName: 'Homer',
  surname: 'Simpson',
};

const fullName = getFullName(character);

console.log(fullName); // => 'Homer Simpson'

It’s worth noting that, as of ES2015, JavaScript now supports arrow function syntax:

const getFullName = (person) => {
return ${person.firstName} ${person.surname};
};

Given our getFullName function has an arity of one (i.e. a single argument) and a single return statement, we can streamline this expression:

const getFullName = person => ${person.firstName} ${person.surname};

These three expressions, despite differing in means, all reach the same end in:

  • creating a function with a name, accessible via the name property, of getFullName
  • accepting a sole parameter, person
  • returning a computed string of person.firstName and person.lastName, both being separated by a space
Combining Functions via Return Values

As well as assigning function return values to declarations (e.g. const person = getPerson();), we can use them to populate the parameters of other functions, or, generally speaking, to provide values wherever JavaScript permits them. Say we have respective functions which perform logging and sessionStorage side effects:

const log = arg => {
console.log(arg);
return arg;
};

const store = arg => {
sessionStorage.setItem('state', JSON.stringify(arg));
return arg;
};

const getPerson = id => id === 'homer'
? ({ firstName: 'Homer', surname: 'Simpson' })
: {};

We can carry out these operations upon getPerson‘s return value with nested calls:

const person = store(log(getPerson('homer')));
// person.firstName === 'Homer' && person.surname === 'Simpson'; => true

Given the necessity of providing the required parameters to functions as they are called, the innermost functions will be invoked first. Thus, in the above example, getPerson‘s return value will be passed to log, and log‘s return value is forwarded to store. Building statements from combined function calls enables us to ultimately build complex algorithms from atomic building blocks, but nesting these invocations can become unwieldy; if we wanted to combine 10 functions, how would that look?

const f = x => g(h(i(j(k(l(m(n(o(p(x))))))))));

Fortunately, there’s an elegant, generic implementation we can use: reducing an array of functions into a higher-order function.


Accumulating Arrays with Array.prototype.reduce

The Array prototype’s reduce method takes an array instance and accumulates it into a single value. If we wish to total up an array of numbers, one could follow this approach:

const sum = numbers =>
numbers.reduce((total, number) => total + number, 0);

sum([2, 3, 5, 7, 9]); // => 26

In this snippet, numbers.reduce takes two arguments: the callback which will be invoked upon each iteration, and the initial value which is passed to said callback’s total argument; the value returned from the callback will be passed to total on the next iteration. To break this down further by studying the above call to sum:

  • our callback will run 5 times
  • since we are providing an initial value, total will be 0 on the first call
  • the first call will return 0 + 2, resulting in total resolving to 2 on the second call
  • the result returned by this subsequent call, 2 + 3, will be provided to the total parameter on the third call etc.

While the callback accepts two additional arguments which respectively represent the current index and the array instance upon which Array.prototype.reduce was called, the leading two are the most critical, and are typically referred to as:

  • accumulator – the value returned from the callback upon the previous iteration. On the first iteration, this will resolve to the initial value or the first item in the array if one is not specified
  • currentValue – the current iteration’s array value; as it’s linear, this will progress from array[0] to array[array.length - 1] throughout the invocation of Array.prototype.reduce
Composing Functions with Array.prototype.reduce

Now that we understand how to reduce arrays into a single value, we can use this approach to combine existing functions into new functions:

const compose = (...funcs) =>
initialArg => funcs.reduce((acc, func) => func(acc), initialArg);

Note that we’re using the rest params syntax (...) to coerce any number of arguments into an array, freeing the consumer from explicitly creating a new array instance for each call site. compose also returns another function, rendering compose a higher-order function, which accepts an initial value (initialArg). This is critical as we can consequently compose new, reusable functions without invoking them until necessary; this is known as lazy evaluation.

How do we therefore compose other functions into a single higher-order function?

const compose = (...funcs) =>
initialArg => funcs.reduce((acc, func) => func(acc), initialArg);

const log = arg => {
console.log(arg);
return arg;
};

const store = key => arg => {
sessionStorage.setItem(key, JSON.stringify(arg));
return arg;
};

const getPerson = id => id === 'homer'
? ({ firstName: 'Homer', surname: 'Simpson' })
: {};

const getPersonWithSideEffects = compose(
getPerson,
log,
store('person'),
);

const person = getPersonWithSideEffects('homer');

In this code:

  • the person declaration will resolve to { firstName: 'Homer', surname: 'Simpson' }
  • the above representation of person will be output to the browser’s console
  • person will be serialised as JSON before being written to session storage under the person key
The Importance of Invocation Order

The ability to compose any number of functions with a composable utility keeps our code cleaner and better abstracted. However, there is an important point we can highlight by revisiting inline calls:

const g = x => x + 2;
const h = x => x / 2;
const i = x => x ** 2;

const fNested = x => g(h(i(x)));

One may find it natural to replicate this with our compose function:

const fComposed = compose(g, h, i);

In this case, why does fNested(4) === fComposed(4) resolve to false? You may remember my highlighting how inner calls are interpreted first, thus compose(g, h, i) is actually the equivalent of x => i(h(g(x))), thus fNested returns 10 while fComposed returns 9. We could simply reverse the invocation order of the nested or composed variant of f, but given that compose is designed to mirror the specificity of nested calls, we need a way of reducing the functions in right-to-left order; JavaScript fortunately provides this with Array.prototype.reduceRight:

const compose = (...funcs) =>
initialArg => funcs.reduceRight((acc, func) => func(acc), initialArg);

With this implementation, fNested(4) and fComposed(4) both resolve to 10. However, our getPersonWithSideEffects function is now incorrectly defined; although we can reverse the order of the inner functions, there are cases where reading left to right can facilitate the mental parsing of procedural steps. It turns out our previous approach is already fairly common, but is typically known as piping:

const pipe = (...funcs) =>
initialArg => funcs.reduce((acc, func) => func(acc), initialArg);

const getPersonWithSideEffects = pipe(
getPerson,
log,
store('person'),
);

By using our pipe function, we will maintain the left-to-right ordering required by getPersonWithSideEffects. Piping has become a staple of RxJS for the reasons outlined; it’s arguably more intuitive to think of data flows within composed streams being manipulated by operators in this order.


Function Composition as an Alternative to Inheritance

We’ve already seen in the prior examples how one can infinitely combine functions into to larger, reusable, goal-orientated units. An additional benefit of function composition is to free oneself from the rigidity of inheritance graphs. Say we wish to reuse logging and storage behaviours based upon a hierarchy of classes; one may express this as follows:

class Storable {
constructor(key) {
this.key = key;
}

store() {
sessionStorage.setItem(
this.key,
JSON.stringify({ ...this, key: undefined }),
);
}
}

class Loggable extends Storable {
log() {
console.log(this);
}
}

class Person extends Loggable {
constructor(firstName, lastName) {
super('person');
this.firstName = firstName;
this.lastName = lastName;
}

debug() {
this.log();
this.store();
}
}

The immediate issue with this code, besides its verbosity, is that we are abusing inheritance to achieve reuse; if another class extends Loggable, it is also inherently a subclass of Storable, even if we don’t require this logic. A potentially more catastrophic problem lies in naming collisions:

class State extends Storable {
store() {
return fetch('/api/store', {
method: 'POST',
});
}
}

class MyState extends State {}

If we were to instantiate MyState and invoke its store method, we wouldn’t be invoking Storable‘s store method unless we add a call to super.store() within MyState.prototype.store, but this would then create a tight, brittle coupling between State and Storable. This can be mitigated with entity systems or the strategy pattern, as I have covered elsewhere, but despite inheritance’s strength of expressing a system’s wider taxonomy, function composition provides a flat, succinct means of sharing code which has no dependence upon method names.


Summary

JavaScript’s handling of functions as values, as well as the expressions which produce them, lends itself to the trivial composition of much larger, context-specific pieces of work. Treating this task as the accumulation of arrays of functions culls the need for imperative, nested calls, and the use of higher-order functions results in the separation of their definition and invocation. Additionally, we can free ourselves of the rigid hierarchical constraints imposed by object-orientated programming.

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JavaScript Tutorial: if-else Statement in JavaScript

JavaScript Tutorial: if-else Statement in JavaScript

This JavaScript tutorial is a step by step guide on JavaScript If Else Statements. Learn how to use If Else in javascript and also JavaScript If Else Statements. if-else Statement in JavaScript. JavaScript's conditional statements: if; if-else; nested-if; if-else-if. These statements allow you to control the flow of your program's execution based upon conditions known only during run time.

Decision Making in programming is similar to decision making in real life. In programming also we face some situations where we want a certain block of code to be executed when some condition is fulfilled.
A programming language uses control statements to control the flow of execution of the program based on certain conditions. These are used to cause the flow of execution to advance and branch based on changes to the state of a program.

JavaScript’s conditional statements:

  • if
  • if-else
  • nested-if
  • if-else-if

These statements allow you to control the flow of your program’s execution based upon conditions known only during run time.

  • if: if statement is the most simple decision making statement. It is used to decide whether a certain statement or block of statements will be executed or not i.e if a certain condition is true then a block of statement is executed otherwise not.
    Syntax:
if(condition) 
{
   // Statements to execute if
   // condition is true
}

Here, condition after evaluation will be either true or false. if statement accepts boolean values – if the value is true then it will execute the block of statements under it.
If we do not provide the curly braces ‘{‘ and ‘}’ after if( condition ) then by default if statement will consider the immediate one statement to be inside its block. For example,

if(condition)
   statement1;
   statement2;

// Here if the condition is true, if block 
// will consider only statement1 to be inside 
// its block.

Flow chart:

Example:

<script type = "text/javaScript"> 

// JavaScript program to illustrate If statement 

var i = 10; 

if (i > 15) 
document.write("10 is less than 15"); 

// This statement will be executed 
// as if considers one statement by default 
document.write("I am Not in if"); 

< /script> 

Output:

I am Not in if
  • if-else: The if statement alone tells us that if a condition is true it will execute a block of statements and if the condition is false it won’t. But what if we want to do something else if the condition is false. Here comes the else statement. We can use the else statement with if statement to execute a block of code when the condition is false.
    Syntax:
if (condition)
{
    // Executes this block if
    // condition is true
}
else
{
    // Executes this block if
    // condition is false
}


Example:

<script type = "text/javaScript"> 

// JavaScript program to illustrate If-else statement 

var i = 10; 

if (i < 15) 
document.write("10 is less than 15"); 
else
document.write("I am Not in if"); 

< /script> 

Output:

i is smaller than 15
  • nested-if A nested if is an if statement that is the target of another if or else. Nested if statements means an if statement inside an if statement. Yes, JavaScript allows us to nest if statements within if statements. i.e, we can place an if statement inside another if statement.
    Syntax:
if (condition1) 
{
   // Executes when condition1 is true
   if (condition2) 
   {
      // Executes when condition2 is true
   }
}

Example:

<script type = "text/javaScript"> 

// JavaScript program to illustrate nested-if statement 

var i = 10; 

if (i == 10) { 

// First if statement 
if (i < 15) 
	document.write("i is smaller than 15"); 

// Nested - if statement 
// Will only be executed if statement above 
// it is true 
if (i < 12) 
	document.write("i is smaller than 12 too"); 
else
	document.write("i is greater than 15"); 
} 
< /script> 

Output:

i is smaller than 15
i is smaller than 12 too
  • if-else-if ladder Here, a user can decide among multiple options.The if statements are executed from the top down. As soon as one of the conditions controlling the if is true, the statement associated with that if is executed, and the rest of the ladder is bypassed. If none of the conditions is true, then the final else statement will be executed.
if (condition)
    statement;
else if (condition)
    statement;
.
.
else
    statement;


Example:

<script type = "text/javaScript"> 
// JavaScript program to illustrate nested-if statement 

var i = 20; 

if (i == 10) 
document.wrte("i is 10"); 
else if (i == 15) 
document.wrte("i is 15"); 
else if (i == 20) 
document.wrte("i is 20"); 
else
document.wrte("i is not present"); 
< /script> 

Output:

i is 20

How to Retrieve full Profile of LinkedIn User using Javascript

How to Retrieve full Profile of LinkedIn User using Javascript

I am trying to retrieve the full profile (especially job history and educational qualifications) of a linkedin user via the Javascript (Fetch LinkedIn Data Using JavaScript)

Here we are fetching LinkedIn data like Username, Email and other fields using JavaScript SDK.

Here we have 2 workarounds.

  1. Configuration of linkedIn developer api
  2. Javascript Code to fetch records

Configuration of linkedIn developer api

In order to fetch records, first we need to create developer api in linkedin which will act as token/identity while fetching data from other linkedin accounts.

So to create api, navigate to https://linkedin.com/developer/apps and click on 'Create Application'.

After navigating, fill in details like name, description and other required fields and then submit.

As we submit, it will create Client ID and Client Secret shown below, which we will be using in our code while communicating to fetch records from other LinkedIn account.

Note: We need to provide localhost Url here under Oauth 2.0. I am using my localhost, but you can probably use other production URLs under Oauth 2.0 where your app is configured. It will make your api  consider the Url as trusted which fetching records.

Javascript Code to fetch records

For getting user details like first name, last name,User image can be written as,

<script type="text/javascript" src="https://platform.linkedin.com/in.js">  
    api_key: XXXXXXX //Client ID  
    onLoad: OnLinkedInFrameworkLoad //Method that will be called on page load  
    authorize: true  
</script>  
<script type="text/javascript">  
    function OnLinkedInFrameworkLoad() {  
        IN.Event.on(IN, "auth", OnLinkedInAuth);  
    }  
  
    function OnLinkedInAuth() {  
        IN.API.Profile("me").result(ShowProfileData);  
    }  
  
    function ShowProfileData(profiles) {  
        var member = profiles.values[0];  
        var id = member.id;  
        var firstName = member.firstName;  
        var lastName = member.lastName;  
        var photo = member.pictureUrl;  
        var headline = member.headline;  
        //use information captured above  
        var stringToBind = "<p>First Name: " + firstName + " <p/><p> Last Name: " + lastName + "<p/><p>User ID: " + id + " and Head Line Provided: " + headline + "<p/>"  
        document.getElementById('profiles').innerHTML = stringToBind;  
    }  
</script>    

Kindly note we need to include 'https://platform.linkedin.com/in.js' as src under script type as it will act on this Javascript SDK provided by Linkedin.

In the same way we can also fetch records of any organization with the companyid as keyword.

<head>  
    <script type="text/javascript" src="https://platform.linkedin.com/in.js">  
        api_key: XXXXXXX ////Client ID  
        onLoad: onLinkedInLoad  
        authorize: true  
    </script>  
</head>  
  
<body>  
    <div id="displayUpdates"></div>  
    <script type="text/javascript">  
        function onLinkedInLoad() {  
            IN.Event.on(IN, "auth", onLinkedInAuth);  
            console.log("On auth");  
        }  
  
        function onLinkedInAuth() {  
            var cpnyID = XXXXX; //the Company ID for which we want updates  
            IN.API.Raw("/companies/" + cpnyID + "/updates?event-type=status-update&start=0&count=10&format=json").result(displayCompanyUpdates);  
            console.log("After auth");  
        }  
  
        function displayCompanyUpdates(result) {  
            var div = document.getElementById("displayUpdates");  
            var el = "<ul>";  
            var resValues = result.values;  
            for (var i in resValues) {  
                var share = resValues[i].updateContent.companyStatusUpdate.share;  
                var isContent = share.content;  
                var isTitled = isContent,  
                    isLinked = isContent,  
                    isDescription = isContent,  
                    isThumbnail = isContent,  
                    isComment = isContent;  
                if (isTitled) {  
                    var title = isContent.title;  
                } else {  
                    var title = "News headline";  
                }  
                var comment = share.comment;  
                if (isLinked) {  
                    var link = isContent.shortenedUrl;  
                } else {  
                    var link = "#";  
                }  
                if (isDescription) {  
                    var description = isContent.description;  
                } else {  
                    var description = "No description";  
                }  
                /* 
                if (isThumbnailz) { 
                var thumbnailUrl = isContent.thumbnailUrl; 
                } else { 
                var thumbnailUrl = "http://placehold.it/60x60"; 
                } 
                */  
                if (share) {  
                    var content = "<a target='_blank' href=" + link + ">" + comment + "</a><br>";  
                    //el += "<li><img src='" + thumbnailUrl + "' alt=''>" + content + "</li>";  
                    el += "<li><div>" + content + "</div></li>";  
                }  
                console.log(share);  
            }  
            el += "</ul>";  
            document.getElementById("displayUpdates").innerHTML = el;  
        }  
    </script>  
</body>  

We can get multiple metadata while fetching records for any any organization. We can get company updates as shown below.

Conclusion

We can also fetch any company specific data like company job updates/post, total likes, comments, and number of views along with a lot of metadata we can fetch which I have shown below.

Thank you for reading !

7 Best Javascript Iframe Libraries

7 Best Javascript Iframe Libraries

Iframes let you build user experiences into embeddable ‘cross-domain components’, which let users interact with other sites without being redirected. I have compiled 7 best Javascript iframe libraries.

Iframes let you build user experiences into embeddable ‘cross-domain components’, which let users interact with other sites without being redirected. I have compiled 7 best Javascript iframe libraries.

1. Zoid

A cross-domain component toolkit, supporting:

  • Render an iframe or popup on a different domain, and pass down props, including objects and functions
  • Call callbacks natively from the child window without worrying about post-messaging or cross-domain restrictions
  • Create and expose components to share functionality from your site to others!
  • Render your component directly as a React, Vue or Angular component!
    It's 'data-down, actions up' style components, but 100% cross-domain using iframes and popups!

Download


2. Postmate

Postmate is a promise-based API built on postMessage. It allows a parent page to speak with a child iFrame across origins with minimal effort.

Download


3. Iframe Resizer

Keep same and cross domain iFrames sized to their content with support for window/content resizing, in page links, nesting and multiple iFrames

Demo

Download


4. Iframely

Embed proxy. Supports over 1800 domains via custom parsers, oEmbed, Twitter Cards and Open Graph

Demo

Download


5. React Frame component

This component allows you to encapsulate your entire React application or per component in an iFrame.

Demo

Download


6. Seamless.js

A seamless iframe makes it so that visitors are unable to distinguish between content within the iframe and content beside the iframe. Seamless.js is a JavaScript library (with no dependencies) that makes working with iframes easy by doing all the seamless stuff for you automatically.

Demo

Download


7. Porthole

A proxy to safely communicate to cross-domain iframes in javascript

Demo

Download


Thank for read!