let length = 16;                               // Number
let lastName = "Johnson";                      // String
let x = {firstName:"John", lastName:"Doe"};    // Object

The Concept of Data Types

In programming, data types is an important concept.

To be able to operate on variables, it is important to know something about the type.

Without data types, a computer cannot safely solve this:

let x = 16 + "Volvo";

Does it make any sense to add "Volvo" to sixteen? Will it produce an error or will it produce a result?

JavaScript will treat the example above as:

let x = "16" + "Volvo";

When adding a number and a string, JavaScript will treat the number as a string.

Example

let x = 16 + "Volvo";

Example

let x = "Volvo" + 16;

JavaScript evaluates expressions from left to right. Different sequences can produce different results:

JavaScript:

let x = 16 + 4 + "Volvo";

Result:

20Volvo

JavaScript:

let x = "Volvo" + 16 + 4;

Result:

Volvo164

In the first example, JavaScript treats 16 and 4 as numbers, until it reaches "Volvo".

In the second example, since the first operand is a string, all operands are treated as strings.

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JavaScript Data Types

The Concept of Data Types

Example

Example

JavaScript:

JavaScript:

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