Functions
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Expert Answer & Key Takeaways
Mastering Functions is essential for high-fidelity technical architecture and senior engineering roles in 2026.
JavaScript Functions
A JavaScript function is a block of code designed to perform a particular task. A function is executed when "something" invokes it (calls it).
1. Function Declarations
A function declaration is defined with the
function keyword, followed by a name, followed by parentheses ().function myFunction(p1, p2) {
return p1 * p2; // The function returns the product of p1 and p2
}2. Function Expressions
A JavaScript function can also be defined using an expression. A function expression can be stored in a variable:
const x = function (a, b) {return a * b};
let z = x(4, 3);The function above is actually an anonymous function (a function without a name).
3. The Function() Constructor
Functions can also be defined with a built-in JavaScript function constructor called
Function().const myFunction = new Function("a", "b", "return a * b");
let x = myFunction(4, 3);[!WARNING] Most of the time, you should avoid using theFunctionconstructor. It is slower and less secure than declarations or expressions.
4. Arrow Functions
Arrow functions allow a short syntax for writing function expressions. They were introduced in ES6 and are the standard in modern 2026 development.
// ES5
var x = function(x, y) {
return x * y;
};
// ES6 / 2026 Standard
const x = (x, y) => x * y;Arrow functions do not have their own
this. They are not well suited for defining object methods.Top Interview Questions
?Interview Question
Q:What is the difference between a function declaration and a function expression?
A:
Function declarations are hoisted, meaning they can be called before they are defined. Function expressions are not hoisted and are only available after the line where they are defined.
?Interview Question
Q:Why use arrow functions?
A:
Arrow functions provide a more concise syntax, especially for simple one-line functions. They also lexically bind the 'this' value, which makes them very useful in callback scenarios (like array methods or React hooks).
?Interview Question
Q:What is an anonymous function?
A:
An anonymous function is a function without a name. They are often used as arguments to other functions or assigned to variables (function expressions).
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