双端队列检测一个词组是否构成回文

class Deque{
    constructor(){
        this.count = 0;
        this.lowestCount = 0;
        this.items = {};
    }
    addBack(element){
        this.items[this.count] = element;
        this.count++;
    }
    isEmpty(){
        return this.count - this.lowestCount === 0;
    }
    size(){
        return this.count - this.lowestCount;
    }
    removeFront(){
        if(this.isEmpty()){
            return undefined;
        }
        const re = this.items[this.lowestCount];
        delete this.items[this.lowestCount];
        this.lowestCount ++;
        return re;
    }
    removeBack(){
        if(this.isEmpty()){
            return undefined;
        }
        this.count --;
        const res = this.items[this.count];
        delete this.items[this.count];
        return res;
    }
}

function palindromeChecker(aString){
    if(aString === undefined || aString === null || (aString !==null && aString.length==0)){
        //检查传入的字符串参数是否合法
        return false;
    }
    
    const deque = new Deque();

    //将所有字母转换为小写并移除空格
    const lowerString = aString.toLocaleLowerCase().split(' ').join('');

    let isEqual = true;
    let firstChar,lastChar;

    for(let i = 0; i < lowerString.length; i++){
        //将lowerString中的字符逐个加入队列中
        deque.addBack(lowerString.charAt(i));
    }

    while(deque.size() > 1 && isEqual){//所有双端队列中元素大于1（一个字符为回文）并且首尾字符相同
        firstChar = deque.removeFront();//从前端移除一个元素
        lastChar = deque.removeBack();//从后端移除一个元素

        //移除的两个字符必须相同
        if(firstChar !== lastChar){
            isEqual = false;
        }
    }
    return isEqual;
} 
console.log('level', palindromeChecker('level'));

console.log('a', palindromeChecker('a')); 
console.log('aa', palindromeChecker('aa')); 
console.log('kayak', palindromeChecker('kayak')); 
console.log('level', palindromeChecker('level')); 
console.log('Was it a car or a cat I saw', palindromeChecker('Was it a car 
or a cat I saw')); 
console.log('Step on no pets', palindromeChecker('Step on no pets'));