用栈实现字符平衡

今天学了数据结构的栈，里面讲了一个用栈实现字符平衡。用JS实现了下

//step1 => declare a stack and a str for test and a flag for final check
var stack=[],
    str="(123)iasd[123]]",
    flag=true;
//step2 => for loop and push the left-part into stack;
strlen=str.length;
for(var i=0;i<strlen;i++){
    if(str[i]==‘(‘ || str[i]==‘[‘){
        stack.push(str[i]);
    }
    //step3 => test if the character is suited to the top of stack;
    var stacklen=stack.length;
    //step4 => suited and pop the top of stack;

   //step5 => not suited and change the flag
    if(str[i]==‘)‘ && stack[stacklen-1]!=‘(‘){
        flag=false;
    }
    if(str[i]==‘]‘ && stack[stacklen-1]!=‘[‘){
        flag=false;
    }

    if(str[i]==‘)‘ && stack[stacklen-1]==‘(‘){
        stack.pop();
    }
    if(str[i]==‘]‘ && stack[stacklen-1]==‘[‘){
        stack.pop();
    }
}
// step6 => after the loop,if the stack have elements,change the flag to false;

if(stack.length){
    flag=false;
}
//step7 => check out flag;
alert(flag);

代码很粗糙，没分装，另外只做到了对()[]的判断。