Is JavaScript a Typed Language?

JavaScript is weakly typed in its nature. This enables us to use implicit type conversion. Take the following for example:

// This will return "12" as 1 will be converted into a string
1 + "2"
typeof (1 + "2") // Will return "string"

// This will return 12 as "12" will be converted into a number
"12" * 1
typeof ("12" * 1) // Will return "number"

Even though we did not specify we wanted to convert the string/number into the other format, JavaScript did it for us implicitly. This is type conversion in action.

So how do you convert different types?

To convert string or any other value to number, use the built-in Number function:

// Converting data to number
Number('123');
Number(true)  // Returns NaN

Alternatively, you can also use parseInt(), but always make sure you pass the radix as a second parameter. Otherwise, you may happen to get unexpected results. You can also check if something is a number using isInteger:

Number.isInteger('123'); // returns false
Number.isInteger(123)    // returns true

To convert data into a string, use the built-in String function:

String('123'); // returns "123"
String(true);  // returns "true"
String(NaN);   // returns "NaN"

Lastly, if you want to conver something into a boolean, use the built-in Boolean function.

Boolean(0);     // returns false
Boolean('');    // returns false
Boolean(NaN);   // returns false

Boolean(1);     // returns true
Boolean(123);   // returns true
Boolean('true') // returns true

You can also simply double negate a variable to get it converted into a true / false value:

!!0   // returns false
!!1   // returns true
!!NaN // returns false

In summary, you can use these three built in methods to convert different types of data:

• Number()
• String()
• Boolean()

50 JavaScript Interview QuestionsAnd their answers explainedHere are 50 JavaScript interview questions that often come up during a technical interview. In one place, one resource to learn from.Learn More

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Resources:

• The typeof operator in JavaScript