如何通过 JavaScript 创建 json for loop？

From what I understand of your request, this should work:

<script>
//  var status  = document.getElementsByID("uniqueID"); // this works too
var status  = document.getElementsByName("status")[0];
var jsonArr = [];


for (var i = 0; i < status.options.length; i++) {
jsonArr.push({
id: status.options[i].text,
optionValue: status.options[i].value
});
}
</script>

var sels = //Here is your array of SELECTs
var json = { };


for(var i = 0, l = sels.length; i < l; i++) {
json[sels[i].id] = sels[i].value;
}

If you want a single JavaScript object such as the following:

{ uniqueIDofSelect: "uniqueID", optionValue: "2" }

(where option 2, "Absent", is the current selection) then the following code should produce it:

  var jsObj = null;
var status = document.getElementsByName("status")[0];
for (i = 0, i < status.options.length, ++i) {
if (options[i].selected ) {
jsObj = { uniqueIDofSelect: status.id, optionValue: options[i].value };
break;
}
}

If you want an array of all such objects (not just the selected one), use michael's code but swap out status.options[i].text for status.id.

If you want a string that contains a JSON representation of the selected object, use this instead:

  var jsonStr = "";
var status = document.getElementsByName("status")[0];
for (i = 0, i < status.options.length, ++i) {
if (options[i].selected ) {
jsonStr = '{ '
+ '"uniqueIDofSelect" : '
+ '"' + status.id + '"'
+ ", "
+ '"optionValue" : '
+ '"'+ options[i].value + '"'
+ ' }';
break;
}
}

Your question is pretty hard to decode, but I'll try taking a stab at it.

You say:

I want to create a json object having two fields uniqueIDofSelect and optionValue in javascript.

And then you say:

I need output like

[{"selectID":2,"optionValue":"2"},
{"selectID":4,"optionvalue":"1"}]

Well, this example output doesn't have the field named uniqueIDofSelect, it only has optionValue.

Anyway, you are asking for array of objects...

Then in the comment to michaels answer you say:

It creates json object array. but I need only one json object.

So you don't want an array of objects?

What do you want then?

Please make up your mind.

If I want to create JavaScript Object from string generated by for loop then I would JSON to Object approach. I would generate JSON string by iterating for loop and then use any popular JavaScript Framework to evaluate JSON to Object.

I have used Prototype JavaScript Framework. I have two array with keys and values. I iterate through for loop and generate valid JSON string. I use evalJSON() function to convert JSON string to JavaScript object.

Here is example code. Tryout on your FireBug Console

var key = ["color", "size", "fabric"];
var value = ["Black", "XL", "Cotton"];


var json = "{ ";
for(var i = 0; i < key.length; i++) {
(i + 1) == key.length ? json += "\"" + key[i] + "\" : \"" + value[i] + "\"" : json += "\"" + key[i] + "\" : \"" + value[i] + "\",";
}
json += " }";
var obj = json.evalJSON(true);
console.log(obj);