Salesforce JavaScript Developer Practice Exam

What will the output be when using eval on the valueOf method of a String object containing '2 + 2'?

1. 4

2. "2 + 2"

3. 2

4. NaN

The correct answer is: 4

When using `eval` on the value of the `valueOf` method from a String object containing '2 + 2', the output will be 4. The `valueOf` method of a String object returns the primitive value of the specified object, which in this case would be the string '2 + 2'. When the `eval` function is called with this string, it evaluates the expression contained within the string. Since '2 + 2' is a valid JavaScript expression, `eval` processes it and computes the result, which is the numeric value 4. In this way, `eval` executes the string as if it were actual JavaScript code, allowing it to perform the addition operation inherent in the expression. Thus, the output is the numerical result of the operation, which is 4.