This blog is dedicated to understand the following JavaScript Concepts:
- Declaration
- Initialization
- Mutability
- Immutability
- Reassignment
Declaration
This is the phase where you tell the JavaScript engine about the variable. For example:
let age;
declares that there is a variable named age.
Initialization
This phase involves assigning a value to the variable. If you do not explicitly initialize the variable at the time of declaration, JavaScript automatically initializes it to undefined
.
let a;
console.log(a);
Output: undefined
Mutability
This refers to the ability to alter the internal state or content of a data structure or object in place. For example, if we have object obj
and you changed a property within it, you would be mutating the object:
let obj = { key: "value" };
obj.key = "new value";
Mutating the object by changing a property
Immutability
Immutability refers to the inability to alter the state or content of a variable after it has been created. When a variable holds an immutable value, any modification results in the creation of a new value rather than changing the original.
let greeting = "Hello";
let newGreeting = greeting.replace("H", "J");
console.log(greeting); // Output: "Hello"
console.log(newGreeting); // Output: "Jello"
In this example:
-
greeting
is a string with the valueHello
. - The replace method creates a new string
newGreeting
with the valueJello
. - The original greeting string remains unchanged.
Immutability ensures that primitive values remain constant, preventing unintended side effects. Any operation that attempts to modify an immutable value creates a new value, leaving the original unchanged.
Reassignment
This refers to the act of assigning a new value to a variable. This action doesn't alter the original value; rather, it updates what the variable points to.
let y = "hello";
y = "world";
Reassigning y to reference a different string
Conclusion
In this topic, we explored key JavaScript concepts: declaration, initialization, mutability, immutability, and reassignment. Understanding these concepts helps in writing clear and predictable code.
- Declaration introduces a variable.
- Initialization assigns an initial value.
- Mutability allows modification of an object's state.
- Immutability prevents changes to a value, ensuring data integrity.
- Reassignment updates the variable's reference without altering the original value.
Grasping these concepts is essential for effective JavaScript programming.
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