Introduction

Control flow is what lets your JavaScript code make decisions. Conditionals like if, else, switch, and logical operators enable branching and complex logic. In this guide you'll learn:

1. Boolean values and truthiness
2. if / if-else statements
3. The ternary operator
4. switch statements
5. Logical operators (&&, ||, !)

Understanding these tools allows you to direct program execution based on conditions.

1. Booleans & Truthiness / Falsiness

1.1 The Boolean Type

In JavaScript, Boolean is a primitive type with exactly two values: true and false. These are used in conditions to drive logic. ([w3schools.com/js/js_booleans.asp])

1.2 Truthy and Falsy Values

Beyond strict Booleans, JavaScript considers certain values as truthy (treated like true) or falsy (treated like false) in conditional contexts:

Falsy values include:

1. false
2. 0
3. "" (empty string)
4. null
5. undefined
6. NaN

Everything else is truthy, e.g. nonempty strings, nonzero numbers, objects, arrays, etc.

Example:

Use truthiness understanding to write cleaner code.

2. The if Statement

The simplest conditional structure in JavaScript is the if statement:

Example:

If the condition evaluates to true, the code block runs; otherwise, it’s skipped.

3. if … else

You can provide an alternative path when the if condition fails:

Example:

4. if … else if … else

To test multiple conditions in sequence:

Example:

5. The Ternary Operator

For concise conditional expressions, JavaScript provides the ternary operator (condition ? exprIfTrue : exprIfFalse). It is useful for simple if-else logic in a single line.

Example:

You can even nest ternary operators, though readability may suffer if overused. ([w3schools.com/js/js_if_ternary.asp])

6. switch Statement

For comparing one value against many possible matches, switch is often cleaner than many else if blocks.

Example:

Important: always include break (unless intentional fallthrough) to prevent execution from continuing into next cases. ([w3schools.com/js/js_switch.asp])

7. Logical Operators: &&, ||, !

Logical operators let you combine or invert Boolean expressions.

1. && (AND) — true if both operands are truthy
2. || (OR) — true if at least one operand is truthy
3. ! (NOT) — negates the truth value

Examples:

Logical operators are essential for combining complex conditions. ([w3schools.com/js/js_logical.asp])

8. Putting It All Together

Example combining multiple concepts:

Best Practices & Tips

1. Use === / !== for comparisons to avoid type coercion surprises.
2. Favor if / else if / else or switch when readability matters.
3. Use the ternary operator only for simple conditions to keep code legible.
4. Avoid overly deep nesting of conditionals—refactor with functions when logic becomes complex.
5. Remember JavaScript’s truthy/falsy rules to avoid unintended behavior.

Conclusion

Conditionals and logical operators are the heart of decision-making in JavaScript. Mastering them enables dynamic, flexible, and robust code paths. Once you are comfortable with these, the next steps are loops, functions, and working with events and the DOM.