令人惊讶的简单操作结果

Question

在JavaScript中，我尝试执行以下语句

var x = 1+"2"-3; //Anser is 9.
var y = 1-"2"+4 //Anser is 3.

对于这样的操作，什么转换为什么？

我猜1+"2" = 12(number)然后是12-3？

Answer 1

-将两个操作数转换为数字。但是，如果+的任一操作数是字符串，则另一个操作数转换为字符串，它是串联的。像"Hi, " + "how are you?" = "Hi, how are you?"那样你的答案是正确的。

var x = 1+"2"-3; 
// concats the string as 12 and then subtracts...
12 - 3 = 9
var y = 1-"2"+4 
// converts to numbers and subtracts, making -1 and then adds 4 giving out 3
-1 + 4 = 3

这是一个过程。

Answer 2

情景I

第1步：

1 + "2" => "12" //concatenation happened

第2步

"12" - 3 => 9 //String widens to number since we are using - symbol here.

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情景II

第1步：

1 - "2" => -1 //String widens to number since we are using - symbol here.

第2步：

-1 + 4 => 3 //Normal addition happens