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setTimeout(function(){
var s,t,o,p,b,r,e,a,k,i,n,g,f, iFhpHCE={"rkBBjKVIpmV":!+[]+!![]+!![]+!![]+!![]+!![]+!![]+!![]+!![]};
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;iFhpHCE.rkBBjKVIpmV+=+((!+[]+!![]+!![]+!![]+[])+(+!![]));iFhpHCE.rkBBjKVIpmV+=+((+!![]+[])+(!+[]+!![]+!![]+!![]+!![]+!![]+!![]+!![]));iFhpHCE.rkBBjKVIpmV-=+!![];iFhpHCE.rkBBjKVIpmV-=+((+!![]+[])+(!+[]+!![]));iFhpHCE.rkBBjKVIpmV-=!+[]+!![]+!![]+!![];iFhpHCE.rkBBjKVIpmV+=+((!+[]+!![]+!![]+!![]+[])+(!+[]+!![]));iFhpHCE.rkBBjKVIpmV+=+((!+[]+!![]+!![]+!![]+[])+(!+[]+!![]+!![]+!![]+!![]+!![]));iFhpHCE.rkBBjKVIpmV-=+((!+[]+!![]+!![]+[])+(!+[]+!![]+!![]));iFhpHCE.rkBBjKVIpmV-=+((!+[]+!![]+!![]+[])+(!+[]+!![]+!![]+!![]+!![]+!![]+!![]));iFhpHCE.rkBBjKVIpmV*=+((+!![]+[])+(+[]));a.value = parseInt(iFhpHCE.rkBBjKVIpmV, 10) + t.length; '; 121'
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Ray ID: 3210f106637a33bb
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就是怪异的计算而已，对象转换之类的，自己log下对应的值就知道是什么了，然后按照js算法自己服务器端写一遍
参考
+/-一元运算符计算空字符结果为0分析
javascript计算不同数据类型如何转换
var s, t, o, p, b, r, e, a, k, i, n, g, f, iFhpHCE = { "rkBBjKVIpmV": !+[] + !![] + !![] + !![] + !![] + !![] + !![] + !![] + !![] };
console.log(!+[] + !![] + !![] + !![] + !![] + !![] + !![] + !![] + !![])// 9
//t = document.createElement('div');
// t.innerHTML="<a href='/'>x</a>";
// t = t.firstChild.href;r = t.match(/https?:\/\//)[0];
// t = t.substr(r.length); t = t.substr(0,t.length-1);
// a = document.getElementById('jschl-answer');
// f = document.getElementById('challenge-form');
; iFhpHCE.rkBBjKVIpmV += +((!+[] + !![] + !![] + !![] + []) + (+!![]));
console.log(+((!+[] + !![] + !![] + !![] + []) + (+!![])))// 41
iFhpHCE.rkBBjKVIpmV += +((+!![] + []) + (!+[] + !![] + !![] + !![] + !![] + !![] + !![] + !![]));
console.log(+((+!![] + []) + (!+[] + !![] + !![] + !![] + !![] + !![] + !![] + !![])))// 18
iFhpHCE.rkBBjKVIpmV -= +!![];
console.log(+!![])// 1
iFhpHCE.rkBBjKVIpmV -= +((+!![] + []) + (!+[] + !![]));
console.log(+((+!![] + []) + (!+[] + !![])))// 12
iFhpHCE.rkBBjKVIpmV -= !+[] + !![] + !![] + !![];
console.log(!+[] + !![] + !![] + !![])//4
iFhpHCE.rkBBjKVIpmV += +((!+[] + !![] + !![] + !![] + []) + (!+[] + !![]));
console.log(+((!+[] + !![] + !![] + !![] + []) + (!+[] + !![])))//42
iFhpHCE.rkBBjKVIpmV += +((!+[] + !![] + !![] + !![] + []) + (!+[] + !![] + !![] + !![] + !![] + !![]));
console.log(+((!+[] + !![] + !![] + !![] + []) + (!+[] + !![] + !![] + !![] + !![] + !![])))//46
iFhpHCE.rkBBjKVIpmV -= +((!+[] + !![] + !![] + []) + (!+[] + !![] + !![]));
console.log(+((!+[] + !![] + !![] + []) + (!+[] + !![] + !![])))//33
iFhpHCE.rkBBjKVIpmV -= +((!+[] + !![] + !![] + []) + (!+[] + !![] + !![] + !![] + !![] + !![] + !![]));
console.log(+((!+[] + !![] + !![] + []) + (!+[] + !![] + !![] + !![] + !![] + !![] + !![])))//37
iFhpHCE.rkBBjKVIpmV *= +((+!![] + []) + (+[]));
console.log(+((+!![] + []) + (+[])))//10
a.value = parseInt(iFhpHCE.rkBBjKVIpmV, 10) + t.length; '; 121'