使用JQUERY的对象中的下一个和上一个项目

Question

I have an object "data" as defined:

MYLIST
    61:
        ALREADY_EXIST: 1
        ARCHIVE: 0
        CODE_UNIT: "F.5"
        GROUP_TYPE: "Group"
        ID: 61
        SG_CODE: "ABCD00"
    62:
        ALREADY_EXIST: 0
        ARCHIVE: 0
        CODE_UNIT: "D.1"
        GROUP_TYPE: "Sub-Group"
        ID: 62
        SG_CODE: "ABCD11"
    86:
        ALREADY_EXIST: 1
        ARCHIVE: 0
        CODE_UNIT: "B.1"
        GROUP_TYPE: "Group"
        ID: 61
        SG_CODE: "ABC235"
    99:
        ALREADY_EXIST: 0
        ARCHIVE: 0
        CODE_UNIT: "A.2"
        GROUP_TYPE: "Group"
        ID: 62
        SG_CODE: "ABCD11"
SUBJECT_CODE_NUMBER: 4

I'm trying to parse this object for displaying value following the previous and nex values.

I would like to retrieve the next and previous element in variables , how can I do that?

$.each(data.MYLIST,function(k,v){       
    alert(v); //OK
    console.log(data.MYLIST[k].SG_CODE); //OK
    console.log(????); // FOR THE NEXT VALUE
    console.log(????); // FOR THE PREVIOUS VALUE                        
});

In Mylist k is not a continuous value. k+1 is not compulsory the following value of k. For example you have the item 62 and after the item is 86.

Thus I cannot use:

var next = data.EXPERT_GROUP[k+1].SG_CODE  
var previous= data.EXPERT_GROUP[k-1].SG_CODE 

In this case do you know a way for getting the next value and the previous value? Thank you in advance for your help.

Seb

Answer 1

With jQuery $.each you can access to the index directly with the first parameter of the function. Assuming your index can't be negative.

var previous = -1;
$.each(data.MYLIST,function(k,v){
    alert(v); //OK

    if(previous != -1){
      console.log(data.MYLIST[previous].SG_CODE); // FOR THE PREVIOUS VALUE
    }
    console.log(data.MYLIST[k].SG_CODE); //OK
    previous = k;                     
});

Should do the trick for the previous one, don't think you can access next value if your index does not increment on a regular basis.

Answer 2

Since your array does not have defined values at continuous index locations, you may define a method like:

function seekNext(a, index) { 
   for(var i = index; i<a.length; i++){
     if(a[i]){ 
       return a[i] }
     }
};

You may invoke this method as seekNext(data.MYLIST, k)

Same way one may write seekPrev implementation too. If the index values of the array are continuous, one could have accessed previous and next values by incrementing and de-incrementing the current array loop index value.

Answer 3

Edit 28/4/17

I overwrite the $.each method.

code

a= {"a":{"c":"1"},"b":{"c":"2"},"c":{"c":"3"},"d":{"c":"4"},"e":{"c":"7"},"f":{"c":"9"}};

$.each = function (obj, callback) {
  var length, i;
  this.preAndNext = 0,
    this.previous = { "index": null, "data": null },
    this.now = { "index": null, "data": null };
  if (obj.length) {
    length = obj.length;
    for (; i < length; i++) {
      if (callback.call(obj[i], i, obj[i]) === false) { break; }
    }
  } else {
    //that's your object need it.
    for (i in obj) {
      if (this.preAndNext) {
        if (callback.call(obj[i], this.now.index, this.previous.data, this.now.data, obj[i]) === false) { break; }
      }
      this.previous = (this.now.data) ? this.now : this.previous;
      this.now = { "index": i, "data": obj[i] };
      this.preAndNext = true;
    }
    callback.call(obj[i], i, (this.now.data ? this.previous.data : null), (this.now.data || this.previous.data), null);
  }
  return obj;
}

$.each(a,function(i,pre,now,next){
  //i:index
  //pre:previous object;
  //now:now state object;
  //next: the next object;
  console.log(i,pre,now,next);
});

Add your code after you call jquery.If your loop encounter first or last that element was rendered null .(ie the first loop pre = null )

Hope to help you.