Salesforce JavaScript Developer Practice Exam

What will be the output when executing this code? let x = 10; const test = (y = (x += 10)) => y; console.log(test());

1. 10

2. 20

3. 30

4. NaN

The correct answer is: 20

The code snippet initializes a variable `x` with the value `10`. The function `test` is defined as an arrow function that takes one parameter `y`. If no argument is passed when `test` is called, `y` will be assigned the result of the expression `(x += 10)`. The expression `x += 10` increments the value of `x` by `10`, changing `x` from `10` to `20`. Since `test()` is called without an argument, the default parameter `y` gets the value of `x`, which is now `20`. The function then returns `y`, which is also `20`. Thus, when `console.log(test())` is executed, it outputs `20`. The logic of how default parameters work in conjunction with variable updates here is key, as it demonstrates the order of operations and the implications of mutating the value of a variable within the context of a function call.