Using the Unary + Operator Before a String and Concatenating It in JavaScript – Asked in a Deloitte Interview.

Understanding the Code Step by Step

The given JavaScript snippet contains a tricky expression that involves string concatenation (+) and unary plus (+). Let’s break it down the code expression.

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Step 1: Understanding the Expression

var str = "abc" + +"def";

Let’s analyze the right-hand side of the assignment:

"abc" + +"def"

This consists of:

1. A string "abc"
2. A string concatenation (+) operation
3. A unary plus (+) applied to "def"

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Step 2: Evaluating the Unary Plus (+)

+"def"

• The unary plus (+) is a JavaScript operator that attempts to convert its operand into a number.
• Here, "def" is a string that does not represent a valid number.
• When JavaScript tries to convert "def" to a number using +, it results in:

NaN  // Not a Number

So, "abc" + +"def" is equivalent to:

"abc" + NaN

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Step 3: Evaluating the String Concatenation

"abc" + NaN

• The + operator, when used with a string, performs string concatenation rather than arithmetic addition.
• "abc" is a string, and NaN is coerced into its string representation, which is "NaN".
• So, "abc" + NaN evaluates to:

"abcNaN"

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Step 4: Assigning the Value

var str = "abcNaN";

Now, str holds the value:

"abcNaN"

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Step 5: Logging the Output

console.log(str);

Console Output:

abcNaN

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🔍 Key Takeaways

1. The unary plus (+) operator attempts to convert "def" into a number but fails, resulting in NaN.
2. The + operator between a string ("abc") and NaN leads to string concatenation, resulting in "abcNaN".

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✨ Conclusion

This code snippet is a classic example of JavaScript’s type coercion!
It demonstrates how the unary plus (+) operator attempts type conversion and how concatenation works when dealing with NaN.

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✔ Final Answer:

C) abcNaN

🔹 This question appeared in the Deloitte 1st round of interview, testing the candidate’s knowledge of string concatenation and the unary plus (+) operator in JavaScript.