+ javascript 中的一元运算符

Question

我已经读过这个主题了： Explain +var and -var unary operator in javascript

但我仍然无法理解这个简单的代码:

var a = 3;
console.log(-a);  // -3
console.log(+a);  //  3
a = -a;
console.log(a);  // -3
console.log(+a);  // -3

"The unary negation operator precedes its operand and negates it."

"The unary plus operator precedes its operand and evaluates to its operand but attempts to converts it into a number, if it isn't already."

但我还是不明白为什么第一次 console.log(+a) return 3。

Answer 1

but i still can't figure why console.log(+a) return 3 the first time.

此时 a 的值为 3。

上一行 -a 采用 a 的 值，取反并将其传递给 console.log。它 不会 将更改后的值分配回 a。