如何访问数组中的javascript键/值对

Question

I have the following javascript array:

var groupedDataSet1 = [{year: "0-1k", value1: Math.floor(Math.random()), value2: Math.floor(Math.random()), value3: Math.floor(Math.random())},
            {year: "1-2k", value1: Math.floor(Math.random()), value2: Math.floor(Math.random()), value3: Math.floor(Math.random())},
            {year: "2-3k", value1: Math.floor(Math.random()), value2: Math.floor(Math.random()), value3: Math.floor(Math.random())},
            {year: "3-4k", value1: Math.floor(Math.random()), value2: Math.floor(Math.random()), value3: Math.floor(Math.random())},
            {year: "4-5k", value1: Math.floor(Math.random()), value2: Math.floor(Math.random()), value3: Math.floor(Math.random())}];

I'd like to programatically know how many key/value pairs I have in each entry.

Is there a way to know that groupedDataSet contains the keys year, value1, value2, and value3 while another javascript array might only contain year, value1 and value2?

Doing groupedDataSet[0].length doesn't work.

Thanks.

Answer 1

Object.keys(groupedDataSet[0]).length

should get you what you're looking for. It returns an array containing the instance keys in the object.

Answer 2

If the objects in the list may have different key set, then you have to check each object to collect all keys. You can do

var keys_memo = {};
groupedDataSet1.forEach(function (item) {
    for (var i in item) {
        keys_memo[i] = 1;
    }
});
var keys = Object.keys(keys_memo);

console.log(keys)
>>>["year", "value1", "value2", "value3"]