javascript - 数组的迭代器

Question

来自JavaScript Iterators

var Iterator = function(arr){ return {
    index : -1,
    hasNext : function(){ return this.index <= arr.length; },
    hasPrevious: function(){ return this.index > 0; },

    current: function(){ return arr[ this["index"] ]; },

    next : function(){
        if(this.hasNext()){
            this.index = this.index + 1;            
            return this.current();
        } 
        return false;
    },

    previous : function(){
        if(this.hasPrevious()){
            this.index = this.index - 1
            return this.current();
        }
        return false;
    }
}   
};

var iter = Iterator([1,2,3]);

我想通过添加动态值来重写此功能

   added : function(data){
          arr.push(data);
          this.index++
        }


iter.added(1);
iter.added(6);
iter.added(7);
iter.added(8);

怎么办呢？我了解 ES 6 中的迭代器 https://developer.mozilla.org/ru/docs/Web/JavaScript/Reference/Global_Objects/Iterator但我想要支持 IE

Answer 1

您需要添加类似于您发布的内容的 added() 函数，然后更新索引的初始值，以便 next() 和 previous() 函数正常工作。您需要将其设置为输入数组长度，以便 next() 函数知道您位于最后一个元素。

var Iterator = function(arr){ return {
    index : arr.length,
    hasNext : function(){ return this.index < arr.length - 1; },
    hasPrevious: function(){ return this.index > 0; },

    current: function(){ return arr[ this.index ]; },

    next : function(){
        if(this.hasNext()){
            this.index = this.index + 1;            
            return this.current();
        } 
        return false;
    },

    previous : function(){
        if(this.hasPrevious()){
            this.index = this.index - 1
            return this.current();
        }
        return false;
    },

    added: function(x){
        arr.push(x);
      this.index++;
    }
}   
};

var iter = Iterator([1,2,3]);
console.log(iter)
iter.added(1);
iter.added(6);
iter.added(7);
iter.added(8);
console.log(iter)
console.log(iter.next())
console.log(iter.previous())
console.log(iter.previous())
console.log(iter.previous())
console.log(iter.previous())
console.log(iter.next())
console.log(iter.current())

哪些输出:

Object {arr: Array[3], index: 3}
Object {arr: Array[7], index: 7}
false
8
7
6
1
6
6

这是在 fiddle 中:https://jsfiddle.net/8ojcrnkn/5/

希望有帮助!