Conditional statements in JavaScript are fundamental programming constructs that control the flow of code execution based on different conditions. They allow programs to make decisions and execute specific blocks of code only when certain conditions are met, making our programs dynamic and responsive.
The if statement is the most basic conditional statement in JavaScript. It executes a block of code only when a specified condition evaluates to true. The syntax is simple: if followed by parentheses containing the condition, then curly braces containing the code to execute. In this example, since age is 18 and 18 is greater than or equal to 18, the condition is true, so the message will be displayed.
The else statement provides an alternative path when the if condition is false. The else if statement allows us to test multiple conditions in sequence, creating decision chains for complex logic. In this grading example, we check conditions from highest to lowest score. Since the score is 85, the first condition fails, but the second condition for grade B is true, so that code executes.
The switch statement provides a cleaner alternative to long if-else chains when comparing a single value against multiple constant values. It evaluates the expression once and compares it with each case. When a match is found, the corresponding code executes. The break keyword is crucial to prevent fall-through to subsequent cases. In this example, since day equals Monday, it matches the first case and executes that code block.
The ternary operator provides a concise way to write simple if-else statements in a single line. It uses the syntax: condition question mark value if true colon value if false. This is particularly useful for simple assignments based on conditions. In summary, JavaScript offers several conditional statements: if for basic conditions, else for alternatives, else if for multiple conditions, switch for comparing against constant values, and the ternary operator for concise conditional assignments. These tools are fundamental for creating dynamic and responsive programs.