How to Convert a String into Boolean in TypeScript?

TypeScript is considered a strongly typed language that assists the users to specify the function, parameter, and variable type. It supports all primitive data types like numbers, Boolean, and strings. The “number” represents the numeric values, the “string” specifies the text data, and the “boolean” denotes the “true/false” value.

In simple terms, each data type stores a specific type of data and serves a special purpose. However, the user can also convert the data from one type to another as per requirements.

This post explains all the possible approaches to convert a string into a boolean in TypeScript. The guideline of this post is as follows:

Let’s start with the “strict equality” Operator

Method 1: Using the “strict equality(===)” Operator

The “strict equality(===)” operator checks whether the specified two operands are equal or unequal and returns the result as a boolean value i.e. true/false. In this example, the “strict equality” operator is applied for converting the specified string into a boolean.

Copy the given lines of code into the file having the “.ts” extension:

const str = 'True';
const bool = str.toLowerCase() === 'true';

In this code:

  • The “str” variable initializes a string quoted in single quotes.
  • Next, the “bool” variable applies the “toLowerCase()” method to convert the initialized string into lowercase and then check whether it is equal to the given operand or not.
  • After that, the “console.log()” method displays the “bool” variable value.

Now, compile the “.ts” file and run the automatically generated “.js” file to see the output using the following commands:

tsc main.ts //Compile
node main.js //Run

The output shows that the specified string has been successfully converted to a boolean value i.e. “true”.

Method 2: Using the Boolean Constructor

The “Boolean()” constructor is also beneficial to convert a string into a boolean. It specifies the string as its argument and then retrieves a boolean value.


const value1 = Boolean('true');

const value2 = Boolean('false');

In the above code block:

  • The “value1” variable uses the “Boolean()” constructor having the string as its argument.
  • The “console.log()” method shows the “value1” variable result.
  • The same procedure is followed for another string stored in the “value2” variable.

Compile “.ts” and run the “.js” file:

tsc main.ts //Compile
node main.js //Run

The above output returns a “true” boolean value for both of the initialized strings.

Method 3: Using the “!!(double exclamation mark)” Operator

The “!!(double exclamation mark)” acts as a double not operator that converts the specified object into a boolean value and returns “true”. Here in this scenario, it is used for the conversion of a string into a boolean.


const str = "false";
const value = !!str;

At this time the “!!” operator is associated with the “str” variable to convert its value i.e. string into boolean.

Execute the compiler and run the “.js” file:

tsc main.ts //Compile
node main.js //Run

The outcome displays that the initialized string has been successfully converted into a boolean i.e. “true”.

Method 4: Using a Regular Expression

The “test()” method of the “Regular” interface allows the user to create a regular expression as per requirement. In this method, it is used to create a “/true/i” regex to convert a string into a boolean. In this regex, the “true” represents a pattern and the “i” specifies the case-insensitive flag.


const str = "true";
const value = (/true/i).test(str);

Here, the created “(/true/i)” regular expression is used with the “test()” method that takes the “str” variable as its argument. As a result, it will convert the given string and retrieve a boolean value.


The output shows a “true” boolean value as a converted string because the specified string matches with the regex pattern “true”.

Method 5: Use the “parse()” Method of JSON

The “parse()” method of the JSON interface helps to transform/parse a JSON string in TypeScript. This scenario uses the stated method to parse the specified string into a boolean.


const str = "true";
const value = JSON.parse(str);

Now, the JSON “parse()” method takes the “str” variable as its argument to parse its string value into a boolean.


The above output shows the converted string into a boolean i.e. “true”.

Method 6: Using a “switch” Statement

The “switch” statement is used to check different cases in TypeScript. Here it is utilized for converting the string into a boolean depending on the cases.


const String:string = 'false';
let value: boolean;
switch(String) {
case 'true':
 value = true;
case 'false':
 value = false;

The above code snippet specifies the “switch” statement which returns the “boolean” type value depending on the specified cases.


The outcome displays the boolean value “false” according to the declared value of the string type.

Method 7: Using a “ternary” Operator

The “ternary” operator refers to a conditional operator that is the simplest/shortest way of specifying an “if-else” statement in TypeScript. In this case, it is used to convert a string into a boolean. Let’s see it practically.


const str = 'false';
const bool = str === 'false' ? true : false;

Here, in the above lines of code:

  • The “ternary” operator first specifies the condition followed by “?(question mark)”, and then the first and second expressions that are separated by a “:(colon)”.
  • If the specified condition becomes “true” the first expression “true” will execute and if the condition becomes “false” then the second “false” expression will execute.


The output returns “true” as a converted string because the specified condition became true.


To convert a “string” into a “boolean” in TypeScript use the “strict equality”, “!!(double exclamation mark)”, and “ternary” operators as well as the “Boolean” constructor. This task can also be performed with the help of the “Regular Expression”, JSON “parse()” method, and the “switch” statement. All of the discussed approaches are quite simple and easy to use. This post explained all possible methods practically to convert a string into a boolean in TypeScript.

About the author

Areej Nadeem

I am a technical author holding a Bachelor’s degree in Computer Science. I am passionate about writing and learning new technologies and sharing my knowledge with the rest of the world.