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Javascript is loosely or dynamically typed language. In loosely typed language, the data type of the variable is checked at run-time and not like strongly typed language where the data type of the variable is checked at the compile-time only. Variables in Javascript don’t hold any fixed data type. A variable assigned a string type can be converted into a string type and vice versa. For example var str = “Hello World !!!”, var str = 12345.

In Javascript, keyword ‘this’ behaves differently based on how a function is called at run time. It can be assigned during execution and its value may be different each time when the function is invoked. The value of ‘this’ is different each type the function is invoked. ECMAscript 5 introduced the bind() function to set the function’s ‘this’ value, regardless of how it is called. ECMAscript2015 introduced the concept of “arrow functions” which don’t provide ‘this’ binding their own but it gets the ‘this’ value of the enclosing text context.

Outside any function, ‘this’ represents any global object regardless of strict mode. 

In Javascript, pass by value refers to the function which is called directly by passing the variable value as argument. Changing the function arguments does not impact the variable passed from outside the function.

In pass by reference, function is called by passing the variable’s address as function argument. Here, changing the function arguments impact the variable passed from outside the function. 

Scope determines the accessibility of the variables, functions, and objects within the Javascript program during runtime. There are four types of scope in Javascript - 

• Global Scope
• Block Scope
• Function Scope
• Local Scope

• Global Scope  - A variable declared outside any function becomes global and can be accessed from anywhere in the Javascript program. 

• Block Scope - The two keywords ‘let’ and ‘const’ introduced by ES6 provide block scope, and variables declared inside {....} are accessed within this block only.

• Function Scope - Variables defined inside a function are not accessible outside the function.

• Local Scope - Local variables have their scope limited to the functions i.e., created when the function starts and deleted when the function ends. 

Scope chain determines the scope for a given function. Each function that is defined  has its own nested scope and the nested function (function defined inside function) has a local scope which is linked to its outside function, this is called scope chain.

When the bind() method is invoked, the JS engine creates a new function and binds the variable as its ‘this’ variable. The call() method invokes a function by explicitly specifying what ‘this’ should point to within the calling function. The difference between bind() and call() is that call() accepts the additional parameters also, and does not make the function’s copy on which it is invoked.

The apply() method works the same as call() method but the only difference is apply() takes an array of parameters to be passed within it while the call() method expects the parameters to be passed individually.

Hoisting in Javascript is the default behavior in which a variable or function is moved to the top of the current scope (scope refers to a script or function) and can be used before declaring them.

For example, console.log(test);

var test;

works as

var test;

console.log(test); The output in both the cases is undefined. 

Currying is the technique of breaking down a function that takes multiple arguments into the function series that take only one argument. 

For example,

function(a,b){ 

return a+b;

}

 can be written as 

function add (a){ 

return function (b); 

return a+b;

 }

Javascript is synchronous in nature as it holds another requests while executing a request. When you run a block of code in Javascript, no other block will be executed on that page at the same time. However, it implements asynchronous handling in its event like in the form of callbacks feature, async/await, and promises

jQuery is a small, fast, and cross-browser compatible library that simplifies tasks like HTML traversal and DOM Manipulation, AJAX calls, JSON parsing, CSS effects and animations, provides extensibility through plugins, and many more.  jQuery binds multiple lines of code into functions that can be invoked only writing one line of code.

If you are trying to hire a Javascript Developer. Here is the Javascript Developer Job Description that you can use in your hiring.