Welcome to Day 6 of your JavaScript learning journey!

If you're serious about mastering JavaScript, it's essential to understand the lingo — the core concepts that keep popping up everywhere in JS tutorials and documentation.

This article is your cheatsheet of essential JavaScript terminologies explained with examples.

🧠 1. Variable

A variable is a container used to store values in memory.

let name = "Dhanian";

🔧 2. Function

A block of reusable code designed to perform a task.

function greet() {
  console.log("Hello!");
}

🌍 3. Scope

Scope determines where a variable is accessible in your code.

  • Global Scope
  • Function Scope
  • Block Scope (with let/const)

⚙️ 4. Execution Context

The environment in which code is executed. There are two main types:

  • Global Execution Context
  • Function Execution Context

Each context has two phases:

  1. Memory Allocation
  2. Code Execution

🧱 5. Call Stack

A stack data structure that keeps track of function calls.

It works on LIFO (Last In, First Out) — the last function pushed onto the stack is the first one to finish.

🔼 6. Hoisting

JS moves declarations (not initializations) to the top of their scope during the memory phase.

console.log(a); // undefined
var a = 10;

🧵 7. Closure

A function that retains access to its lexical scope even when executed outside that scope.

function outer() {
  let count = 0;
  return function inner() {
    count++;
    console.log(count);
  }
}
const counter = outer();
counter(); // 1
counter(); // 2

🪝 8. Callback

A function passed into another function as an argument to be executed later.

function runTask(callback) {
  callback("Task Complete");
}
runTask(console.log);

🔮 9. Promise

Represents a value that may be available now, later, or never.

const promise = new Promise((resolve, reject) => {
  resolve("Success!");
});

🕓 10. Async / Await

A cleaner way to work with Promises.

async function fetchData() {
  let result = await promise;
  console.log(result);
}

👤 11. This

Refers to the object that is currently executing the function.

const user = {
  name: "Dhanian",
  greet() {
    console.log("Hi, I'm " + this.name);
  }
};
user.greet();

🔁 12. Event Loop

The mechanism that handles asynchronous code in JavaScript. It works with:

  • The Call Stack
  • The Task Queue (Callback Queue)

📊 13. Data Types

  • Primitive: string, number, boolean, null, undefined, symbol, bigint
  • Non-Primitive: object, array, function

♻️ 14. Type Coercion

JavaScript converts values automatically during operations.

"5" + 1   // "51"
"5" - 1   // 4

✅ 15. Truthy and Falsy Values

  • Falsy: false, 0, "", null, undefined, NaN
  • Everything else is Truthy

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✅ Next up: Stay tuned for Day 7 → JavaScript Data Types Cheatsheet

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