获取url地址？后面的key值

function getQueryString(str, key) {
if(str) {
var queryString = str.split('?')[1] || '';
var arr = queryString.split('&') || [];
for(var i = 0; i<arr.length; i++) {
var keyString = decodeURIComponent(arr[i].split('=')[0]);
var valueString = decodeURIComponent(arr[i].split('=')[1]);
if(key === keyString) {
return valueString;
}
}
return;
} else {
return;
}
}
getQueryString(location.search, 'backUrl');