This content originally appeared on DEV Community and was authored by Ruhul Amin Sujon
Javascript:
- Closure
- Prototype
- Event loop
async await
Execution context: :(
js code run krlei EC create hobe): two parts.
a. Memory component ( Variable Environment): stored variables and functions as key value pairs
b. Code component ( Thread of execution ): code
2. Execution context phases: Running Javascript code creates an execution context. Execution context is created in two phases.
a. Creation phase ( Memory creation phase )
b. Execution phase ( Code execution phase )
3. Call Stack: To manage Global and Local execution contexts, javascript uses a stack which is called Call-Stack (execution context stack, program stack, control stack, run time stack, machine stack).
4. Hoisting:
a. Arrow function behaves like a variable
b. In creation phase variables are assigned undefined
c. function name stores the whole function body as value
Not Definedmeans the variable is not defined, andundefinedmeans the variable is not assigned value.Javascript is a loosely types or weakly typed language.
7. Scope: it means where we can access a specific variable or function in our code. Scope is directly dependent on the Lexical Environment.
8. Lexical Environment: Lexical environment is the local memory of execution context along with the lexical environment of it’s parent. (lexical means ‘in hierarchy’ or ‘in sequence’)
function a() {
var b = 10;
c();
function c() {
}
}
a()
Now we can say, c function is lexically sitting in a function. or c is hierarchically inside in a.
9. Scope chain: The way javascript searches for variables from it’s local memory to the lexical environment of it’s parent, is called scope chain. Or the chain of lexical environments is called scope chain.
10. Temporal Dead Zone: Temporal dead zone is the time since when the let variable is hoisted and till it is initialized some value. At the time of temporal dead zone, if we try to access a variable, it will give us a reference error.
11. Block: Block is defined by { } these curly braces. It is also known as Compound statement. In block let and const variables are stored in block scope, but var variables are stored in global scope. So we say, let & const are in block scoped.
12. Shadowing: Variable shadowing refers to the practice of naming two variables – for example, a global and local variable or a local variable and a callback function parameter – with the same name and within scopes that overlap.
13. Closure: Function along with its lexical environment forms a closure. When a function is returned from a function, the returned function still keeps it’s lexical scope.
14. Differences: Function statement, function expression, function declaration, anonymous function, Named function expression, parameters vs arguments, first class function, arrow function
- Call stack is in JS engine and JS enfine is the browser. The browser is powerdun. It has the following features:
a. Timer
b. Geo location
c. Url
d. Console
e. Local storage etc.
To access these, Browsers provide some web apis. Those are:
a. SetTimeout()
b. Dom apis (document.*)
c. Fetch()
d. localStorage
e. console
f. location
we can get these web apis in the Call Stack because of the Global object. Global object is Window in the browser.
16. Callback Queue or Task Queue: The callback function of the setTimeout is registered in a browser. When the timer of the browser understands that the time is expored, the callback function is passed to the callback queue.
17. Event Loop: It is ultimately a checker, just checks the callback queue whether there is anything to execute. Then if the call stack is empty, it passed that item wrapping with an execution context to be executed on call stack.
18. Microtask queue: It is similar to callback queue. But it has a higher priority than the callback queue. Callback functions of fetch api are passed to the microtask queue.
19. Microtasks: All the callback functions returned from promises are microtasks. They are passed to the mocrotask queue.
20. Starvation of callback functions: If a callback function from microtask queue creates another microtask and that creates another microtask and that goes on, the callback function of the callback queue is never executed. This scenario is called starvation of callback function in the callback queue.
Short Syllabus
1. Data Structure:
a. Linked list
b. Double linked list
c. Binary search tree
d. Stack
e. Queue
2. Algorithm:
a. Time complexity
b. Space complexity
c. Selection sort (Time complexity & space complexity)
d. Insertion sort (Time complexity & space complexity)
e. Bubble sort (Time complexity & space complexity)
f. Merge sort (Time complexity & space complexity)
g. Quick sort (Time complexity & space complexity)
3. Database
a. Er diagram
b. Various keys(foreign key,primary,unique,candidate,composite key)
c. Relation:
i. One to one
ii. One to many
iii. Many to one
iv. Many to many
d. Join:
i. Left inner join
ii. Right inner join
iii. Cross join
iv. Outer join
e. Transaction
f. Trigger
g. Function
h. Indexing
4. OOP
a. Encapsulation
b. Inheritance
c. polymorphism
d. Compile time polymorphism vs run time polymorphism
e. abstraction
f. Abstract class
g. Access modifier
h. Multiple inheritance vs multilevel inheritance
i. Interface
j. Overloading vs overriding
5. Networking
a. Network 7 layer
b. Tcp vs udp
c. Application of tcp vs udp
This content originally appeared on DEV Community and was authored by Ruhul Amin Sujon
Ruhul Amin Sujon | Sciencx (2025-04-24T15:06:39+00:00) JS IQ – Level 1 – Part 2 (Pondit). Retrieved from https://www.scien.cx/2025/04/24/js-iq-level-1-part-2-pondit/
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