JavaScript Expressions
Literals, Operators, and Evaluation Flow

What is a JavaScript Expression?

In JavaScript, an expression is any piece of code that produces a value. Whether it’s as simple as a number, a string, or something more complex involving functions and operations — if it returns a value, it’s an expression.

Why Are Expressions Important?

Expressions are the building blocks of logic in JavaScript. Without them, statements can’t do anything meaningful. They fuel conditionals, loops, function calls — virtually every line of code depends on them.

1. Types of JavaScript Expressions

1.1 Literal Expressions

Literals are the simplest form of expressions — they represent fixed values.

42
"Hello World"
true
null

These are values themselves — directly usable.

1.2 Arithmetic Expressions

These use arithmetic operators to evaluate numbers.

5 + 3 * 2

11

Note: Operator precedence applies — multiplication before addition.

1.3 String Expressions

Combining strings using the + operator.

"Hello" + " " + "World"

"Hello World"

1.4 Logical Expressions

Involve logical operators &&, ||, and ! for boolean logic.

true && false

false

1.5 Assignment Expressions

These not only assign a value but are themselves expressions that return the value assigned.

let x = 10;
let y = (x = 20);

x is now 20, and y is also 20

1.6 Function Expressions

You can define functions as expressions — especially common with anonymous and arrow functions.

const greet = function(name) {
  return "Hello " + name;
}

greet("Alice") returns "Hello Alice"

1.7 Conditional (Ternary) Expressions

Shortcut for if-else logic.

let age = 18;
let status = (age >= 18) ? "Adult" : "Minor";

"Adult"

2. Expression vs Statement

An expression produces a value. A statement performs an action.

// Expression
3 + 4

// Statement
let result = 3 + 4;

3. Advanced Concepts in Expressions

3.1 Expression as Function Arguments

function double(n) {
  return n * 2;
}

console.log(double(4 + 1));

10

The expression 4 + 1 is evaluated before being passed to double.

3.2 Expressions in Template Literals

let name = "Eva";
let greeting = `Hi, ${name.toUpperCase()}!`;
console.log(greeting);

Hi, EVA!

3.3 Grouping Expressions with Parentheses

Use parentheses to alter the default precedence.

(5 + 3) * 2

16

3.4 Immediately Invoked Function Expressions (IIFE)

Wrap a function expression and call it instantly.

(function() {
  console.log("IIFE executed!");
})();

IIFE executed!

4. Evaluating Expressions Dynamically

JavaScript's eval() can evaluate strings as expressions — though it should be avoided in production due to security risks.

let result = eval("10 + 5");
console.log(result);

15

5. Tips for Understanding and Using Expressions

• Every time you write a value, you’re writing an expression.
• Every operation that results in a value is an expression.
• Function arguments, array elements, object values — they’re all built using expressions.