A “dictionary” refers to a type of data structure that contains key-value pairs in an unordered list. It is equivalent to “map” in TypeScript. It is a useful tool for handling data in TypeScript applications. The process of declaring and initializing a dictionary in TypeScript is simple and easy. The dictionary is commonly declared and initialized in TypeScript using the “Record” utility type.
This post will describe the methods for declaring and initializing a dictionary in Typescript.
How to Initialize and Declare a Dictionary in TypeScript?
To initialize and declare a dictionary in TypeScript, use the following approaches:
Before moving ahead, first understand that for executing a TypeScript file, it must be transpile into a JavaScript file after every modification and then run the JavaScript code on the terminal using the given commands:
node dictionary.js
Method 1: Initialize and Declare Dictionary in TypeScript Using an Indexed Object
To initialize and declare a dictionary, use the “indexed object”. It is a data structure that links a group of keys to a group of values, where each key is distinct and links to a particular value.
Syntax
The following syntax is utilized for initializing and declaring a dictionary using the indexed object:
[key: type]: valueType
};
Example
First, we will define a dictionary named “MyDictionary” which is an indexed object type that describes the shape of our dictionary:
[key: string]: number
};
Then, we declare and initialize a new variable “ageDictionary” of type “MyDictionary” and assign an object literal to it, with three key-value pairs:
"John": 26,
"Mary": 28,
"Rock": 27
};
Print the dictionary on the console by passing the variable in the “console.log()” method:
Output
If you want to retrieve the value of any specified key of a dictionary then, you can use the square bracket notation “[ ]”:
The output displays the age of “Rock” that is “27”:
Method 2: Initialize and Declare Dictionary in TypeScript Using an Interface
For initializing and declaring a dictionary, you can use the “interface”. An interface in TypeScript is a technique for expressing a contract that an object must follow. It defines the attributes and types of properties that an object requires in order to be considered an instance of that interface.
Syntax
Follow the given syntax for initializing and declaring a dictionary using interface:
key1: value1Type;
key2: value2Type;
}
Example
First, define a dictionary named “Info” using an “interface” which requires any object that implements it to have a name property of “string” type and an age property of “number” type:
name: string;
age: number;
}
Then, declare and initialize a new variable “studentDictionary” of type “Info” with an attribute “id” of type “number”:
1: { name: "Jack", age: 15 },
2: { name: "Linta", age: 18 }
};
Lastly, print the dictionary on the console:
Output
Now, we will access the object at index or id 2:
Output
Method 3: Initialize and Declare Dictionary in TypeScript Using ES6 Map
You can also use the ES6 Map approach for initializing and declaring a dictionary in TypeScript. It is a built-in data structure in JavaScript and TypeScript that enables storing key-value pairs, where the key and the value can be of any data type.
Syntax
For using ES6 Map, follow the given syntax:
Example
First, we will create a map object using Map constructor by specifying the type of keys and values as “string”:
Now, utilize the set() method to add the key-value pairs to the dictionary:
student.set("age", "18");
student.set("hobby", "Book Reading");
Print the dictionary on the console:
Output
Method 4: Initialize and Declare Dictionary in TypeScript Using Record Utility Type
Another way to initialize and declare a dictionary is to use the “Record” utility type in TypeScript. It is the most common way of initializing and declaring a dictionary. It is a pre-built data structure in TypeScript that enables creating a type with specified keys and values.
Syntax
The following syntax is used for the Record utility type:
Example
In the given example, we declare and initialize a dictionary called “student” using the “Record” utility type to specify the keys and values of type string:
"name": "Linta",
"age": "18",
"hobby": "Book Reading",
};
Finally, print the dictionary on the console:
Output
We have compiled all the essential information related to the initializing and declaring a dictionary in TypeScript.
Conclusion
To initialize and declare a dictionary in TypeScript, use the “Indexed object”, “an Interface”, “ES6 Map” or the “Record utility type”. The most common way of initializing and declaring a dictionary is the “Record utility type”. This post described the methods for declaring and initializing a TypeScript dictionary.
