JavaScript中的对象访问与数组访问

Question

I have a series of data and the size of it increases gradually. I want to find a specific row of my data with its Id. I have two options. first: create an array and push every new row to this array and every time I want a row just search through items in the array or use array prototype function (find). the other option is to create an object and every time a new row comes just add this row as a property (and the property name would be the Id of the row). and when I want to find a row just get the property of this object by its name(Id). Now I want to know which option is the most efficient way? (or is there a third option?)

first option:

const array = [  
       {  
          "Id":15659,
          "FeederCode":169,
          "NmberOfRepetition":1
       },
       {  
          "Id":15627,
          "FeederCode":98,
          "NmberOfRepetition":2
       },
       {  
          "Id":15557,
          "FeederCode":98,
          "NmberOfRepetition":1
       }
    ]

each time a new row comes a new is pushed into this array. access : array.find(x => x.Id === 15659)

second option:

const object =   {  
       15659:{  
          "Id":15659,
          "FeederCode":169,
          "NmberOfRepetition":1
       },
       15627:{  
          "Id":15627,
          "FeederCode":98,
          "NmberOfRepetition":2
       },
       15557:{  
          "Id":15557,
          "FeederCode":98,
          "NmberOfRepetition":1
       }
    }

each time a new row comes a new property is added to this object. access : object[15659]

edit: I read somewhere that adding new properties to existing object has too much cost.

Answer 1

In case you are looking forward to perform search operation then you should use Object as it gives better performance as compared to search in Array .

Complexity of search in Object is O(1) and in Array is O(n) . Hence, to yield better performance, you should use Object .

Answer 2

Well in the first example you will have to iterate the array every time, when using Find.

In the second example you will be accessing a property directly, leading to O(1) execution time, always fixed, no matter how many items are in there. So for better performance you ought to go by your 2nd way

Answer 3

Reading from objects is faster and takes O(1) time, like @NikhilAggarwal Just said. But recently I was reading about V8 optimizations and wanted to check, so used benchmark js for confirmation.

Here are my findings -

Number of entries in obj or arr : 100000

1. Number of fetch operations from Obj: 47,174,859 ops/sec
2. Number of search operation from Array: 612 ops/sec

If we reduce the entries - The number of operations for object almost remains the same but increases exponentially for arrays.

Number of entries in obj or arr : 100

1. Number of fetch operations from Obj: 44,264,116 ops/sec
2. Number of search operation from Array: 520,709 ops/sec

Number of entries in obj or arr : 10

1. Number of fetch operations from Obj: 46,739,607 ops/sec
2. Number of search operation from Array: 3,611,517 ops/sec