How to parse JSON string in Typescript?
Last Updated : 26 Apr, 2024
In this tutorial, we will learn how we can parse a JSON string in TypeScript. The main reason for learning about it is to learn how we can explicitly type the resulting string to a matching type. The JSON.parse() method will be used to parse the JSON string by passing the parsing string as a parameter to it.
Syntax:
JSON.parse(parsingString);
We can type the parsed string with an explicit type using the following methods:
Typing parsed string using the type alias
The type alias will be used to define a new type with a mixture of different typed properties and can be used to type the parsed string.
Example: The below example will show how you can explicitly type the parsed string using type alias.
JavaScript const jsonStr1 = '{"name": "GeeksforGeeks", "desc": "A Computer Science Portal for Geeks"}'; const jsonStr2 = '{"name": "Google", "desc": "Searching Platform", "workforce": 2000}'; type parseType = { name: string, desc: string, workforce?: number, }; const parsedStr1: parseType = JSON.parse(jsonStr1); const parsedStr2: parseType = JSON.parse(jsonStr2); console.log(`Company Name: ${parsedStr1.name}, Description: ${parsedStr1.desc}`); console.log(`Company Name: ${parsedStr2.name}, Description: ${parsedStr2.desc}, Work Force: ${parsedStr2.workforce}`); Output:
Company Name: GeeksforGeeks, Description: A Computer Science Portal for Geeks Company Name: Google, Description: Searching Platform, Work Force: 2000
Typing parsed string using interfaces
The interfaces can also be used to type the parsed string to the required type as shown in the below example.
Example: This example shows the parsing of JSON string using interface.
JavaScript const jsonStr1 = '{"name": "GeeksforGeeks", "desc": "A Computer Science Portal for Geeks"}'; const jsonStr2 = '{"name": "Google", "desc": "Searching Platform", "workforce": 2000}'; interface parseInterface { name: string; desc: string; workforce?: number; } const parsedStr1: parseInterface = JSON.parse(jsonStr1); const parsedStr2: parseInterface = JSON.parse(jsonStr2); console.log(`Company Name: ${parsedStr1.name}, Description: ${parsedStr1.desc}`); console.log(`Company Name: ${parsedStr2.name}, Description: ${parsedStr2.desc}, Work Force: ${parsedStr2.workforce}`); Output:
Company Name: GeeksforGeeks, Description: A Computer Science Portal for Geeks Company Name: Google, Description: Searching Platform, Work Force: 2000
Typing parsed array string
An array string can also be parsed using the parse method and required to be typed as an explicit array of required types.
Syntax:
const parsedString = JSON.parse(string) as createdType[];
Example: The below example will explain how to type an parsed array string.
JavaScript const jsonStr = `[ {"name": "GeeksforGeeks", "desc": "A Computer Science Portal for Geeks"}, {"name": "Google", "desc": "Searching Platform", "workforce": 2000} ]`; type parsedType = { name: string, desc: string, workforce?: number } const parsedStr = JSON.parse(jsonStr) as parsedType[]; console.log(`Company Name: ${parsedStr[0].name}, Description: ${parsedStr[0].desc}`); console.log(`Company Name: ${parsedStr[1].name}, Description: ${parsedStr[1].desc}`); Output:
Company Name: GeeksforGeeks, Description: A Computer Science Portal for Geeks Company Name: Google, Description: Searching Platform, Work Force: 2000
Typing parsed string using classes
Using classes is another effective way to parse JSON strings in TypeScript. We can define a class that represents the structure of the JSON data, providing type safety and better organization.
Example: Below is an example illustrating the parsing of a JSON string using a class-based approach.
JavaScript class Company { name: string; desc: string; workforce?: number; constructor(name: string, desc: string, workforce?: number) { this.name = name; this.desc = desc; this.workforce = workforce; } } const jsonStr1 = '{"name": "GeeksforGeeks", "desc": "A Computer Science Portal for Geeks"}'; const jsonStr2 = '{"name": "Google", "desc": "Searching Platform", "workforce": 2000}'; const parsedStr1 = JSON.parse(jsonStr1); const parsedStr2 = JSON.parse(jsonStr2); const parsedCompany1: Company = new Company(parsedStr1.name, parsedStr1.desc); const parsedCompany2: Company = new Company(parsedStr2.name, parsedStr2.desc, parsedStr2.workforce); console.log(`Company Name: ${parsedCompany1.name}, Description: ${parsedCompany1.desc}`); console.log(`Company Name: ${parsedCompany2.name}, Description: ${parsedCompany2.desc}, Work Force: ${parsedCompany2.workforce}`); Output:
Company Name:
GeeksforGeeks,
Description:
A Computer Science Portal for Geeks
Company Name:
Google,
Description: Searching Platform,
Work Force: 2000
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