Comments (4)
补充上面
(!"world", !!"from here!!") == !!"from here!!"
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var x = !!"Hello" + (!"world", !!"from here!!"); -> var x = true + true -> var x = 1+1 -> x=2
from frontend-interview.
var x = !!"Hello" + (!"world", !!"from here!!");
等同于 var x= true+(false,true),
MDN 中逗号运算符,对它的每个操作对象求值(从左至右),然后返回最后一个操作对象的值。
因此等同于 var x= true+ true=2
from frontend-interview.
不会报错,输出为2;
原因:var x = !!"Hello" + (!"world", !!"from here!!");
因为这三个字符串都有取反运算符!
,所以可以转化为布尔值,式子可以变形为
var x = true + ( false , true )
然后因为括号,所以先计算( false , true ),又因为里面有逗号运算符,所以输出true,式子变成了
var x = true + true
因为有+
运算符,所以true被转化为数字1,所以最后结果x的值为2
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