JavaScript How to Convert JSON String to Object

Use JSON.parse(jsonString) to convert a JSON string into a JavaScript object.

Examples

Input"{\"name\":\"Alice\",\"age\":25}"

Output{"name":"Alice","age":25}

Input"[1,2,3,4]"

Output[1,2,3,4]

Input"true"

Outputtrue

How to Think About It

To convert a JSON string to an object, you need to use a built-in method that reads the string and creates the matching JavaScript data structure. The method reads the string format and turns it into an object, array, or primitive value depending on the content.

Algorithm

1

Get the JSON string input.

2

Use the built-in JSON parsing method to read the string.

3

Return the resulting JavaScript object or value.

Code

javascript

const jsonString = '{"name":"Alice","age":25}';
const obj = JSON.parse(jsonString);
console.log(obj);
console.log(obj.name);
console.log(obj.age);

Output

{"name":"Alice","age":25}
Alice
25

Dry Run

Let's trace converting '{"name":"Alice","age":25}' to an object.

1

Input JSON string

{"name":"Alice","age":25}

2

Parse string with JSON.parse

Converts string to { name: 'Alice', age: 25 }

3

Access object properties

obj.name is 'Alice', obj.age is 25

Step	Action	Value
1	Input string	{"name":"Alice","age":25}
2	After JSON.parse	{"name":"Alice","age":25} (object)
3	Access obj.name	Alice
4	Access obj.age	25

Why This Works

Step 1: Parsing JSON string

The JSON.parse method reads the JSON string and converts it into a JavaScript object or value.

Step 2: Creating JavaScript object

The method creates an object with keys and values matching the JSON string structure.

Step 3: Using the object

You can now access properties like obj.name or obj.age as normal JavaScript object properties.

Alternative Approaches

Using eval (not recommended)

javascript

const jsonString = '{"name":"Alice","age":25}';
const obj = eval('(' + jsonString + ')');
console.log(obj);

This works but is unsafe and can run malicious code, so avoid using eval for JSON parsing.

Using a try-catch block with JSON.parse

javascript

const jsonString = '{"name":"Alice","age":25}';
let obj;
try {
  obj = JSON.parse(jsonString);
  console.log(obj);
} catch (e) {
  console.error('Invalid JSON string');
}

This safely handles invalid JSON strings by catching errors.

Complexity: O(n) time, O(n) space

Time Complexity

Parsing the JSON string requires reading each character once, so it takes linear time relative to the string length.

Space Complexity

The method creates a new object in memory proportional to the size of the JSON string.

Which Approach is Fastest?

Using JSON.parse is the fastest and safest built-in method. Alternatives like eval are slower and unsafe.

Approach	Time	Space	Best For
JSON.parse	O(n)	O(n)	Safe and fast JSON string to object conversion
eval	O(n)	O(n)	Unsafe, avoid for JSON parsing
Try-catch with JSON.parse	O(n)	O(n)	Safe parsing with error handling