请快速答出此题的答案并解释：var x, y = 1; x + y = ?

The answer is NaN (Not a Number).

Here's why:

1. Variable Declaration and Assignment:

   • var x, y = 1; declares both x and y. However, only y is initialized to 1. x remains undefined.

2. Addition with undefined:

   • When JavaScript performs x + y, it's adding undefined (the value of x) to 1 (the value of y). In JavaScript, undefined plus a number results in NaN.

3. Invalid Assignment:

   • The most crucial point is that x + y = ... is not a valid assignment in JavaScript. You're trying to assign a value to the result of an addition, which isn't a variable. This would cause a runtime error in a browser or other JavaScript environment. If you were trying to assign the sum back to x, you would write x = x + y; or the shorthand x += y;

If the code were intended to initialize both x and y to 1, it should have been var x = 1, y = 1;. Then x + y would correctly evaluate to 2.