身份证18位最后一位计算函数

function checkIdCard(IdCrad){
var ratioArr = [7,9,10,5,8,4,2,1,6,3,7,9,10,5,8,4,2]
var IdCradArr = IdCrad.split("");
var sum = 0;
for(var i=0;i<IdCradArr.length-1;i++){
sum += IdCradArr[i]*ratioArr[i];
}
var lastNumArr = [1,0,'X',9,8,7,6,5,4,3,2];
lastNum = lastNumArr[sum%11];
console.log(IdCradArr[IdCradArr.length-1])
if(lastNum == IdCradArr[IdCradArr.length-1]){
console.log('success');
}
}