Understanding Conditional Statements in JavaScript

The question above focuses on variable assignments within conditional statements. The correct answer to the question "What is the value of "elem" variable?" is "undefined" represented as a string, which is 'undefined'.

Working through the Problem

To understand why this is the correct answer, let's dissect the JavaScript code.

var elem;
if (11 == 11 && 12 < 10) {
    elem = 12;
} else {
    elem = "undefined";
}

The elem variable is initially declared with no value. The if statement then checks two conditions: whether 11 equals 11 and whether 12 is less than 10. The logical operator && requires both conditions to be true for the entire statement to be true.

While the first condition is true(11 does equal 11), the second condition isn't true (12 is not less than 10). Since one condition is false, the entire if statement is false. The else part of the statement is automatically executed, assigning elem the string value "undefined".

Understanding the Value "undefined"

The answer may be a little tricky since both "undefined" and the number 12 are options. "Undefined" in JavaScript usually indicates a variable that has been declared but has no assigned value. However, in this case, elem is assigned the string value "undefined", which isn't the same as the undefined data type.

It's important to note the quotation marks around "undefined" show it's being assigned as a string, which is different from the special undefined variable type in JavaScript.

Best Practices

When working with JavaScript, it's recommended to clearly distinguish between different data types to avoid confusion. Using the string "undefined" instead of the real undefined value can be misleading as they aren't the same. The former is a text string while the latter is a special value type in JavaScript proving absence or non-existence of a value.

Finally, remember that && operator requires all conditions to be true to return true. Here, since one condition is false, the if statement returns false, leading to the execution of the else block.