Expressions Produce Values

An expression evaluates to a value that a statement can use. Multiplication groups before addition; parentheses can change that grouping. Distinguish the calculated value from the instruction that displays it.

Before this topic, review Operators and Comparisons if its terms are unfamiliar.

This is JavaScript using language features and the host console. Read the initial values, then follow each operation to its displayed result. A declaration names a value, a function call performs an operation, and console.log displays its arguments.

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.

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.

1.1 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"

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

// Expression
3 + 4

// Statement
let result = 3 + 4;

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!

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

• 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.

Grouping is not the same as changing every evaluation-order rule. Avoid expressions with several hidden mutations.

Your task: Replace 10 with 20. Predict the result before running the edited program.

The source is repeated here. If the edit targets the HTML rather than the script, use the markup repeated below; the worked answer also repeats the changed markup.

Without parentheses the product is added to 20; with parentheses 25 is multiplied by 2.

An expression evaluates to a value that a statement can use. Multiplication groups before addition; parentheses can change that grouping. Distinguish the calculated value from the instruction that displays it.

Check your variation against this explanation: Without parentheses the product is added to 20; with parentheses 25 is multiplied by 2.

Use the JavaScript array reference library for individual array operations and boundary tests to check a rule independently.