javascript - = +_ 在 JavaScript 中是什么意思

Question

我想知道 = +_ 运算符在 JavaScript 中的含义。它看起来像是在做作业。

例子:

hexbin.radius = function(_) {
   if (!arguments.length)
       return r;
   r = +_;
   dx = r * 2 * Math.sin(Math.PI / 3);
   dy = r * 1.5;
   return hexbin;
};

Answer 1

r = +_;

• + 尝试将任何 _ 转换为数字。
• _ 只是一个变量名(不是运算符)，它可以是 a、foo 等。

示例:

+"1"

将“1”转换为纯数字 1。

var _ = "1";
var r = +_;

r 现在是 1，而不是 "1"。

此外，根据 MDN page on Arithmetic Operators :

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. [...] It can convert string representations of integers and floats, as well as the non-string values true, false, and null. Integers in both decimal and hexadecimal ("0x"-prefixed) formats are supported. Negative numbers are supported (though not for hex). If it cannot parse a particular value, it will evaluate to NaN.

还要注意

unary plus is the fastest and preferred way of converting something into a number