Terms you need to know as JS Developer

Terms you need to know as JS Developer

In this article, we will focus specifically on things you need to know about JavaScript to get up and going as a JS developer.

In this article, we will focus specifically on things you need to know about JavaScript to get up and going as a JS developer.

Values and Types

JavaScript is dynamic typed, meaning variables can hold values of any type without any type enforcement. The following build-in types are available :

  1. string
  2. number
  3. boolean
  4. null and undefined
  5. object
  6. symbol (new to ES6)

JavaScript has typed values, not typed variables, that means a variable in JavaScript can contain any data. A variable can at one moment be a string and at another be a number:

var a;
typeof a;           // "undefined"
typeof a;           // "number"
typeof a;           // "string"

<em>typeof null</em>* is an interesting case because it errantly returns “object” when you’d expect it to return “null”.*#### Objects

Objects are used to store keyed collections of various data and more complex entities, where you can set properties that hold their own values.

Properties can either be accessed with dot notation (i.e., obj.a) or bracket notation (i.e., obj[“a”]). Dot notation is shorter and generally easier to read and is thus preferred when possible.

var obj = {
 a: "js",
 b: 2
obj.a;             // "js"
obj["b"];          // 2


An array is an object that holds values (of any type) not particularly in named properties/keys, but rather in numerically indexed positions. For example:

var arr = ["js", 2, true];
arr[0];            // "js" 
arr[1];            //  2
arr[2];            //  true

Build-In Type Methods

JavaScript provides different data types to hold different types of values. There are two types of data types in JavaScript:

  1. Primitive values
  2. Non-primitive values (object references)

When can have properties and method on non-primitive value.

But how can we length as property and, toUpperCase() as a method on primitive value?

const a = "hello world";
a.length;                   // 11
a.toUpperCase();            // "HELLO WORLD"
typeof a;                   // "string"

When you use a primitive value like “a” as an object by referencing a property or method (e.g., a.toUpperCase() in the previous snippet), JS automatically “boxes” the value to its object wrapper counterpart (hidden under the covers). A string value can be wrapped by a String object, a number can be wrapped by a Number object, and a boolean can be wrapped by a Boolean object.

“Boxing*” is wrapping an object around a primitive value. For instance, > <em>new Number(42)</em> creates a Number object for the primitive number 42.*#### Truthy & Falsy

The specific list of “falsy” values in JavaScript is as follows:

• “ “ (empty string)

• 0, -0, NaN (invalid number)

• null, undefined

• false

Any value that’s not on this “falsy” list is “truthy.” For example : [ ], [1,2,3],

{}, “hello”, 2, {a: 7}.


There are four equality operators: ==, ===,(Equality) and !=, !== (inEquality).

The difference between == and === is usually characterized that == checks for value equality and === checks for both value and type equality. However, this is inaccurate. The proper way to characterize them is that == checks for value equality with coercion allowed, and === checks for value equality without allowing coercion;

=== is often called “strict equality” and == is “loose equality” for this reason.

***Coercion ***is the process of converting value from one type to another (such as string to number, object to boolean, and so on). It comes in two forms : explicit an implicit.
Example of explicit coercion:

var a = “42”; 
var b = Number( a );
a;          // “42” 
b;         // 42 — the number!

Example of implicit coercion:

var a = “42”; 
var b = a * 1;     // “42” implicitly coerced to 42 here
a;  // “42” 
b; // 42 — the number!


The <, >, <=, and >= operators are used for inequality, referred to in the specification as “relational comparison.”

They will be used with comparable values like numbers. But JavaScript string values can also be compared for inequality.

var a = 42; 
var b = "foo";
var c = "53";
var d = "boo" ;
a < c       // true or false ?
a < b;      // true or false ? 
a > b;      // true or false ?
a == b;     // true or false ?
b > d;      // true or false ?

What should be the answer to the above inequality expression? False or True ??

Before finding the solution of the above, let see how two string or number and string are compared.

If both values in the < comparison are strings, as it is with b > d, the comparison are made lexicographically (aka alphabetically like a dictionary).

Similar to the equality operator, coercion is applied to the inequality operators as well. If one or both is not a string, as it is with a < b, then both values are coerced to be numbers, and a typical numeric comparison occurs.

a < c       // true       convert "53" to 53,  42 < 53
a < b;      // false	  convert "foo to NaN, 42 < Nan
a > b;      // false      convert "foo to NaN, 42 >Nan
a == b;     // false      interpreted as 42 == NaN or "42" == "foo"
b > d;      // true       f come after b in alphabetic order

When converting “foo” into a number we get “invalid number value” NaN and NaN is neither greater than nor less than any other value.

Function Scopes

You use the var keyword to declare a variable that will belong to the current function scope, or the global scope if at the top level outside of any function.

We have two more keywords for variable declaration: let and const. They are block scope.

When JavaScript compiles all of your code, all variable declarations using <em>var</em> are hoisted/lifted to the top of their functional/local scope (if declared inside a function) or to the top of their global scope (if declared outside of a function) regardless of where the actual declaration has been made. This is what we mean by “hoisting”.

Functions declarations are also hoisted, but these go to the very top, so will sit above all of the variable declarations.

var myName = ‘Sunil’;
What will be the answer - 
1. Uncaught ReferenceError: myName is not defined
2. Sunil
3. undefined

In the above example, the answer will be — undefined. Why ?? As we mentioned earlier, variables get moved to the top of their scope when your Javascript compiles at runtime. So when the Javascript gets compiled, var myName would get moved to the top of its scope.

The only thing that gets moved to the top is the variable declarations , not the actual value given to the variable.
So that’s why we get undefined, not a ReferenceError because variable declared at the top of the scope.


Closure is one of the most important, and often least understood, concepts in JavaScript. A closure is a function defined inside another function (called parent function) and has access to the variable which is declared and defined in the parent function scope.

The closure has access to the variable in three scopes:

  • Variable declared in his own scope
  • Variable declared in parent function scope
  • Variable declared in the global namespace
function makeAdder(x) {    
// parameter `x` is an inner variable
// inner function `add()` uses `x`, so   
// it has a "closure" over it    
	function add(y) {        
		return y + x;    
    return add; 
var plusTen = makeAdder( 10 );
plusTen( 3 );       // 13 <-- 10 + 3 
plusTen( 13 );      // 23 <-- 10 + 13

When we call makeAdder(10), we get back a reference to its inner add(..) that remembers x as 10. We call this function reference plusTen(..) it adds its inner y( 3 ) to the remembered by x( 10 ).

this Identifier

Another very commonly misunderstood concept in JavaScript is the *this *keyword. If a function has a this reference inside it, that this reference usually points to an object. But which object it points to depends on how the function was called. It’s important to realize that this does not refer to the function itself, as is the most common misconception.

function foo() {    
   console.log( this.bar ); 
var bar = "global";
var obj1 = {    
  bar: "obj1",    
  foo: foo 
var obj2 = {  
  bar: "obj2" 
foo();              // global
obj1.foo();         // "obj1" 
foo.call( obj2 );   // "obj2" 
new foo();          // undefined

To understand what this points to, you have to examine how the function in question was called. It will be one of those four ways just shown above, and that will then answer what this is.


When you reference a property on an object, if that property doesn’t exist, JavaScript will automatically use that object’s internal prototype reference to find another object to look for the property on. You could think of this almost as a fallback if the property is missing.

The internal prototype reference linkage from one object to its fallback happens at the time the object is created. The simplest way to illustrate it is with a built-in utility called Object.create(..).

var foo = {
    a: 42 
// create `bar` and link it to `foo` 
var bar = Object.create( foo );
bar.b = "hello world";
bar.b;      // "hello world" 
bar.a;      // 42 <-- delegated to `foo`

All the terms we have discussed till now (are in brief ) to become a good JS developer you need to become familiar with these terms.

You can start reading the official JS documentation to learn all these concepts in dept.

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.
   // 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,


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

Flow chart:


<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> 


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.
if (condition)
    // Executes this block if
    // condition is true
    // Executes this block if
    // condition is false


<script type = "text/javaScript"> 

// JavaScript program to illustrate If-else statement 

var i = 10; 

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

< /script> 


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.
if (condition1) 
   // Executes when condition1 is true
   if (condition2) 
      // Executes when condition2 is true


<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"); 
	document.write("i is greater than 15"); 
< /script> 


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)
else if (condition)


<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"); 
document.wrte("i is not present"); 
< /script> 


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 type="text/javascript">  
    function OnLinkedInFrameworkLoad() {  
        IN.Event.on(IN, "auth", OnLinkedInAuth);  
    function OnLinkedInAuth() {  
    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;  

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.

    <script type="text/javascript" src="https://platform.linkedin.com/in.js">  
        api_key: XXXXXXX ////Client ID  
        onLoad: onLinkedInLoad  
        authorize: true  
    <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>";  
            el += "</ul>";  
            document.getElementById("displayUpdates").innerHTML = el;  

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


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!


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.


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



4. Iframely

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



5. React Frame component

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



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.



7. Porthole

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



Thank for read!