How to create dictionary and add key–value pairs dynamically?

Last Updated : 28 May, 2020

In this article, we will discuss how we can create a dictionary in JavaScript and add key-value pairs in it. Actually there is no ‘dictionary’ type in JavaScript but we can create key-value pairs by using JavaScript Objects. Create a new JavaScript Object which will act as dictionary.

Syntax: Key can be a string , integer. If you just write key1 or any number, it will treat as a string.

var dict = { key1 : value1 , 
             key2 : value2 , 
             .... 
           };

Create empty dictionary
```
var dict = {};
```
Adding Key-Value Pairs in Dictionary
```
dict[new_key] = new_value;
```
or
If new_key is already present in the dictionary then the value of this will be updated to new_value.
```
dict.new_key = new_value;
```

Accessing Key-Value Pairs

var value = dict[key];

var value = dict.key;

Iterating the whole dictionary

for(var key in dict) {
   console.log(key + " : " + dict[key]);
}

Example:

HTML

<!DOCTYPE html> 
<html> 
    <head> 
        <title>Dictionary in Javascript</title> 
    </head> 
    <body style="text-align: center;"> 
        <h1 style="color: green;"> 
            GeeksforGeeks 
        </h1> 
        <p> 
            var dict = { <br /> 
            "geek" : 1 , <br /> 
            "for" : "2", <br /> 
            "geeks" : 3.5 <br /> 
            }; <br /> 
        </p> 
  
  
        <button onClick="fun()"> 
            Add new Key-Value Pairs 
        </button> 
  
        <p id="demo"></p> 
  
  
        <!-- Script to create dictionary  
                and add key-value pairs -->
        <script> 
            function fun() { 
                var dict = { 
                    geek: 1, 
                    for: "2", 
                    geeks: 3.5, 
                }; 
  
                dict.new_geeks = "new_value"; 
                dict["another_new_geeks"] =  
                "another_value"; 
  
                var to_show = "var dict = { <br>"; 
  
                for (var key in dict) { 
                    to_show += '"' + key + '" : '  
                    + dict[key] + "<br>"; 
                } 
  
                to_show += " }; <br>"; 
  
                document.getElementById("demo") 
                .innerHTML = to_show; 
            } 
        </script> 
    </body> 
</html>                     