为什么（{} + {}）=" [object Object] [object Object]"？ [英] why ({}+{})="[object Object][object Object]"?
问题描述
我测试了代码：
{}+{} = NaN;
({}+{}) = "[object Object][object Object]";
为什么添加（）更改结果？
推荐答案
{} + {} 是阻止后跟一个表达式。第一个 {} 是块（就像你附加到 if 语句的那种）， + {} 是表达式。第一个 {} 是一个块，因为当解析器查找语句并看到 {时，它会将其解释为一个街区的开放。那块空了，什么也没做。处理完块后，解析器会看到 + 并将其读作一元 + 。这将解析器转移到处理表达式。在表达式中， {启动对象初始值设定项而不是块，因此 {} 是对象初始值设定项。对象初始值设定项创建一个对象， + 然后尝试强制转换为一个数字，得到 NaN 。
{}+{} is a block followed by an expression. The first {} is the block (like the kind you attach to an if statement), the +{} is the expression. The first {} is a block because when the parser is looking for a statement and sees {, it interprets it as the opening of a block. That block, being empty, does nothing. Having processed the block, the parser sees the + and reads it as a unary +. That shifts the parser into handling an expression. In an expression, a { starts an object initializer instead of a block, so the {} is an object initializer. The object initializer creates an object, which + then tries to coerce to a number, getting NaN.
在（{} + {}）中，开头（转移解析器进入它期望表达式而不是语句的模式。所以（）包含带有二进制<的两个对象初始值设定项/ em> + （例如，加法运算符，可以是算术或字符串连接）。二进制 + 运算符将尝试根据其操作数添加或连接。它将操作数强制转换为基元，在 {} 的情况下，它们每个都成为字符串[object Object]。所以你最终得到[object Object] [object Object]，结果连接它们。
In ({}+{}), the opening ( shifts the parser into the mode where it's expecting an expression, not a statement. So the () contains two object initializers with a binary + (e.g., the "addition" operator, which can be arithmetic or string concatenation) between them. The binary + operator will attempt to add or concatenate depending on its operands. It coerces its operands to primitives, and in the case of {}, they each become the string "[object Object]". So you end up with "[object Object][object Object]", the result of concatenating them.
这篇关于为什么（{} + {}）=" [object Object] [object Object]"？的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！
