Statement vs Expression in JavaScript

Understanding the difference between statements and expressions is essential to grasp the flow and logic of JavaScript code.

1. Expression

An expression produces a value. It can be used wherever a value is expected.

• Examples:

  // Arithmetic expression
  2 + 2
  
  // String expression
  "Hello" + " World"
  
  // Function call expression
  Math.max(5, 10)
  
  // Boolean expression
  5 > 3

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  Expressions can be part of a larger expression:

  let sum = (2 + 3) * 5; // Expression `2 + 3` is evaluated to 5

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2. Statement

A statement performs an action. It is a complete unit of execution but does not return a value directly.

• Examples:

  // Variable declaration (statement)
  let x;
  
  // Conditional statement
  if (x > 0) {
    console.log("x is positive");
  }
  
  // Loop statement
  for (let i = 0; i < 5; i++) {
    console.log(i);
  }

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Statements typically control the flow of the program (e.g., loops, conditionals) and do not produce values directly.

Key Differences

Aspect	Expression	Statement
Produces a Value	Yes	No
Used in Assignments	Can be assigned to variables	Cannot be directly assigned
Purpose	Evaluates to produce a result	Executes a piece of logic or action
Example	2 + 3, "Hello" + "World"	if, for, let x = 5

Mixing Statements and Expressions

In JavaScript, expressions can be part of statements, but statements cannot be part of expressions. For instance:

// Expression within a statement
let result = (2 + 3) * 5; // The expression `(2 + 3)` evaluates to 5

// Statement
if (result > 10) {
  console.log("The result is greater than 10"); // Statement inside if block
}

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Conclusion

• Use expressions when you need a value or a computation.
• Use statements for actions like defining logic, controlling flow, or declaring variables.