Salesforce JavaScript Developer Practice Exam

What will be the output of the following code: console.log(x); var x = 10;

1. 10

2. undefined

3. ReferenceError

4. NaN

The correct answer is: undefined

In the provided code snippet, the output of `console.log(x); var x = 10;` will indeed be `undefined`. This behavior is a result of JavaScript's variable hoisting mechanism. When the JavaScript engine processes the code, it first hoists the declaration of the variable `x`, which means it acknowledges that `x` exists before it reaches the line where it is logged to the console. However, the assignment of `10` to `x` occurs only after the `console.log` call. So, at the time of the `console.log` execution, `x` has been declared but not yet initialized, leading it to have the value `undefined`. To summarize, JavaScript hoisting allows variable declarations to be lifted to the top of their containing function or scope, so even though `var x = 10;` appears later, `x` is recognized as a declared variable when `console.log(x);` is executed, resulting in an output of `undefined`.