为什么一个对象大于/小于或等于另一个对象? [英] Why is an object greater/less than or equal to a different object?

问题描述

这可能只是JavaScript的怪癖，但我很好奇是否有人知道为什么会发生这种情况:

This might just be a weird quirk of JavaScript, but I'm curious if anyone knows why this happens:

({}< = {})=>是

({}> = {})=>是

({} == {})=>错误

({} === {})=>错误

({}> {})=>错误

({}< {})=>错误

鉴于其他两个均为假，为什么前两个为真?

Why are the first two true given that all the others are false?

我认为可能是在比较之前将对象转换为数字，但是...

I thought it may be casting the objects to numbers before comparing, but...

Number({})> = Number({})=>错误

推荐答案

使用< /< = /> /ES5中的> = 运算符使用抽象关系比较算法" ，这是一种在比较类型之前将其强制转换的好方法.当 {} 与 [[ToPrimitive]] 强制转换时，它会退回到 toString()方法，该方法返回"[object Object]".因为小于/大于运算符的equals-variant首先检查相等性，并且字符串相等，所以检查成功.对于非相等检查变体，它失败了，因为字符串相等.

Using the </<=/>/>= operators in ES5 uses the Abstract Relational Comparison Algorithm, which is a fancy way of saying it coerces the types before comparing them. When {} is coerced with [[ToPrimitive]], it falls back to the toString() method, which returns "[object Object]" for both. Because the equals-variants of the less than/greater than operators check equality first, and the strings are equal, the check succeeds. It fails for the non-equality-checking variants because, well, the strings are equal.

== 不使用相同的强制算法，而是使用

== doesn't use the same coercion algorithm, it uses the Abstract Equality Comparison Algorithm. The first thing this algorithm checks is if the types are the same -- which they are, of course, for two bare objects. Therefore the algorithm proceeds with the first step, and goes down to check f:

如果x和y指向同一个对象，则返回true.否则，返回false.

Return true if x and y refer to the same object. Otherwise, return false.

每次使用 {} 都会创建一个新对象，因此此检查失败，结果为false.

Each usage of {} creates a new object, so this check fails and the result is false.

=== 类似，除了没有强制步骤.它在步骤7 处失败，该步骤使用相同的方法语言作为AECA的子步骤f.

=== is similar, except there is no coercion step. It fails at step 7, which uses the same language as substep f of the AECA.

tl; dr:> = /< = 以不同于 == / ===的方式强制转换.

tl;dr: >= / <= coerce in a different way than == / ===.

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