JavaScript Comparisons and Conditionals Review

# --interactive-- ## Comparisons and the `null` and `undefined` Data Types - **Comparisons and `undefined`**: A variable is `undefined` when it has been declared but hasn't been assigned a value. It's the default value of uninitialized variables and function parameters that weren't provided an argument. `undefined` converts to `NaN` in numeric contexts, which makes all numeric comparisons with `undefined` return `false`. :::interactive_editor ```js console.log(undefined < 0); // false (NaN < 0 is false) console.log(undefined >= 0); // false (NaN >= 0 is false) ``` ::: - **Comparisons and `null`**: The `null` type represents the intentional absence of a value. `null` converts to `0` in numeric contexts, which may result in unexpected behavior in numeric comparisons: :::interactive_editor ```js console.log(null < 0); // false (0 < 0 is false) console.log(null >= 0); // true (0 >= 0 is true) ``` ::: - When using the equality operator (`==`), `null` and `undefined` only equal each other and themselves: :::interactive_editor ```js console.log(null == undefined); // true console.log(null == 0); // false console.log(undefined == NaN); // false ``` ::: - However, when using the strict equality operator (`===`), which checks both value and type without performing type coercion, `null` and `undefined` are not equal: :::interactive_editor ```js console.log(null === undefined); // false ``` ::: ## `switch` Statements - **Definition**: A `switch` statement evaluates an expression and matches its value against a series of `case` clauses. When a match is found, the code block associated with that case is executed. A `break` statement should be placed at the end of each case, to terminate its execution and continue with the next. The `default` case is an optional case and only executes if none of the other cases match. The `default` case is placed at the end of a `switch` statement. :::interactive_editor ```js const dayOfWeek = 3; switch (dayOfWeek) { case 1: console.log("It's Monday! Time to start the week strong."); break; case 2: console.log("It's Tuesday! Keep the momentum going."); break; case 3: console.log("It's Wednesday! We're halfway there."); break; case 4: console.log("It's Thursday! Almost the weekend."); break; case 5: console.log("It's Friday! The weekend is near."); break; case 6: console.log("It's Saturday! Enjoy your weekend."); break; case 7: console.log("It's Sunday! Rest and recharge."); break; default: console.log("Invalid day! Please enter a number between 1 and 7."); } ``` :::