为什么答案是42？ [英] Why is the answer 42?

问题描述

我试图理解这个回文表达式是如何给出的。我知道运算符优先级规则，但这超出了我当前的Javascript级别。我该如何开始？

I'm trying to understand how this palindrome expression is giving 42. I know about operator precedence rules, but this is beyond my current Javascript level. How can I start?

alert ("The answer is " +

[(0>>(0==0))+([0]+[(0==0)+(0==0)]^0)]*[(0^[(0==0)+(0==0)]+[0])+((0==0)<<0)]

);

推荐答案

基本要素如下：

0==0

这是 true ，可以强制转换为 1 。

This is true, which can be coerced in to 1.

a >> b

右移运营商。在这种情况下，它仅在表达式的开头用作 0>> 1 评估为 0 。

The right-shift operator. In this case, it's only used at the beginning of the expression as 0 >> 1 which evaluates to 0.

a^b

按位异或。上述两种用法都有 a 或 b 0 ，因此结果是非零操作数，强制转换为整数。

Bitwise XOR. Both usages above have either a or b are 0, and so the result is the non-zero operand, coerced into an integer.

[a] + [b]

添加 a 和的字符串b ，评估为ab;如果 a 和 b 都是数字（例如 [0] + [1] 结果可以强制转换为数字。

String addition of a and b, evaluates to "ab"; if both a and b are numeric (e.g. [0]+[1] the result can be coerced into a numeric.

[a] * [b]

显然可以在单个元素数组上执行乘法。这相当于 a * b 。

Multiplication can be performed on single element arrays, apparently. So this is equivalent to a*b.

最后，

a << b

左移运算符;对于正整数，这有效地乘以2到幂 b 。在上面的表达式中，它与 b = 0 一起使用，因此结果为 a ，强制转换为整数。

The left-shift operator; for positive integers this effectively multiplies by 2 to the power of b. In the expression above, this is used with b = 0, so the result is a, coerced into an integer.

如果你应用了正确的操作顺序，你就会得到 [ 2] * [21] 评估为 42 。

If you apply the correct order of operations, you get out [2] * [21] which evaluates to 42.

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