Data Type

In computer science and computer programming, a data type or simply type is an attribute of data which tells the compiler or interpreter how the programmer intends to use the data. Most programming languages support basic data types of integer numbers (of varying sizes), floating-point numbers (which approximate real numbers), characters and Booleans. A data type constrains the values that an expression, such as a variable or a function, might take. This data type defines the operations that can be done on the data, the meaning of the data, and the way values of that type can be stored. A data type provides a set of values from which an expression (i.e. variable, function, etc.) may take its values. A value’s data type also affects which operations are valid on that value. For example, an integer can be multiplied by an integer, but not by a string.

Almost all programming languages explicitly include the notion of data type, though different languages may use different terminology.

Common data types include:

• Integer
• Floating-point number
• Character
• String
• Boolean

Static Typing

A statically-typed language is a language (such as Java, C, or C++) where variable types are known at compile time by compiler. In most of these languages, types must be expressly indicated by the programmer; in other cases (such as OCaml), type inference allows the programmer to not indicate their variable types.

Dynamic Typing

Dynamically-typed languages are those (like Python, JavaScript) where the interpreter assigns variables a type at runtime based on the variable’s value at the time.

Primitive

The primitive (primitive value, primitive data type) is data that is not an object and has no methods.

Most of the time, a primitive value is represented directly at the lowest level of the language implementation.

All primitives are immutable, i.e., they cannot be altered. It is important not to confuse a primitive itself with a variable assigned a primitive value. The variable may be reassigned a new value, but the existing value can not be changed in the ways that objects, arrays, and functions can be altered.

Type Conversion

Type conversion (or typecasting) means transfer of data from one data type to another. Implicit conversion happens when the compiler automatically assigns data types, but the source code can also explicitly require a conversion to take place. For example, given the instruction 5 + 2.0, the floating point 2.0 is implicitly typecasted into an integer, but given the instruction Number("0x11"), the string "0x11" is explicitly typecasted as the number 17.

Type Coercion

Type coercion is the automatic or implicit conversion of values from one data type to another (such as strings to numbers). Type conversion is similar to type coercion because they both convert values from one data type to another with one key difference — type coercion is implicit whereas type conversion can be either implicit or explicit.

For example,

const value1 = '5';
const value2 = 9;
let sum = value1 + value2;

console.log(sum);

In the above example, JavaScript has coerced the 9 from a number into a string and then concatenated the two values together, resulting in a string of "59". JavaScript had a choice between a string or a number and decided to use a string.

The compiler could have coerced the 5 into a number and returned a sum of 14, but it did not. To return this result, you’d have to explicitly convert the 5 to a number using the Number() method:

sum = Number(value1) + value2;