Salesforce JavaScript Developer Practice Exam

What will be the output of sum(1, '2') in JavaScript?

1. NaN

2. TypeError

3. "12"

4. 3

The correct answer is: "12"

In JavaScript, when you use the `sum` function, which is likely performing addition here, it will evaluate the operands based on their types according to the rules of type coercion. In the case of `sum(1, '2')`, you have a number (`1`) and a string (`'2'`). When JavaScript encounters the addition operation with these mixed types, it converts the number to a string before performing the operation. This is because the presence of a string in an arithmetic operation triggers a conversion of other operands to string types. As a result, the number `1` is converted to the string `'1'`, and then concatenated with the string `'2'`. This concatenation results in the string `'12'`. This behavior is a fundamental aspect of JavaScript, which allows for flexible type conversions. Therefore, the output of `sum(1, '2')` will be the string `"12"`.