js中利用两个栈实现队列的算法

var s1 = [], s2 = [];
function transferStack(a, b) {
 while(a.length !== 0){
 b.push(a.pop());
 }
}
function push(val) {
 if(s1.length === 0 && s2.length !== 0){
 transferStack(s2, s1);
 }

 s1.push(val);
}

function pop(){
 if(s1.length !== 0 && s2.length === 0){
 transferStack(s1, s2);
 }

 return s2.pop();
}