Salesforce JavaScript Developer Practice Exam

What does eval do when a valid JavaScript expression is passed to it as a string?

1. It executes the string as code.

2. It returns 'undefined'.

3. It compiles the string into an object.

4. It produces a SyntaxError if invalid.

The correct answer is: It executes the string as code.

The function eval is a JavaScript built-in that interprets a string as JavaScript code and executes it. When a valid JavaScript expression is passed to eval as a string, it effectively runs that string as if it were JavaScript code integrated into your script, allowing the evaluation of expressions and execution of statements. For instance, if the string passed is "2 + 2", eval will compute that expression and return the result, which would be 4. This ability to execute code dynamically can be powerful, but it also poses security risks if user input is involved, as it can potentially lead to code injection vulnerabilities. While there are other functions and behaviors in JavaScript associated with the other options, they do not accurately describe what eval does. It's also important to keep in mind that if an invalid expression is passed, eval would indeed throw a SyntaxError, but that does not pertain to the function's behavior when presented with a valid JavaScript expression. Thus, the essence of eval’s purpose and function is best captured by stating that it executes the string as code.