Introduction to DataTypes and Values

We'll start with an article that describes how a computer stores values and some primitive types such as numbers and strings. You can think of the "type of a value" as defining how it is stored, named, and manipulated. For example, a calculator program uses the type "number", which holds "numeric values" and supports "arithmetic operations". JavaScript has two types: "primitive" and "object". Examples of primitive types include numbers, strings, and Booleans. Object types include arrays, objects, and functions.

Here are some things to remember when using JavaScript data types:

  • Primitive types are "immutable"; their "values" cannot be changed once created;
  • Object types are "mutable"; their values can change once created; and
  • Although JavaScript supports types, it is a "dynamically typed" language, which means that you do not have to define the type of variable in a JavaScript program (but this is not a best practice).

Values, Types, and Operators

"Below the surface of the machine, the program moves. Without effort, it expands and contracts. In great harmony, electrons scatter and regroup. The forms on the monitor are but ripples on the water. The essence stays invisibly below".

- Master Yuan-Ma, The Book of Programming

Inside the computer's world, there is only data. You can read data, modify data, create new data – but that which isn't data cannot be mentioned. All this data is stored as long sequences of bits and is thus fundamentally alike.

Bits are any kind of two-valued things, usually described as zeros and ones. Inside the computer, they take forms such as a high or low electrical charge, a strong or weak signal, or a shiny or dull spot on the surface of a CD. Any piece of discrete information can be reduced to a sequence of zeros and ones and thus represented in bits.

For example, we can express the number 13 in bits. It works the same way as a decimal number, but instead of 10 different digits, you have only 2, and the weight of each increases by a factor of 2 from right to left. Here are the bits that make up the number 13, with the weights of the digits shown below them:

 0     0   0   0   1   1   0   1
 128  64  32  16   8   4   2   1

So that's the binary number 00001101. Its non-zero digits stand for 8, 4, and 1, and add up to 13.

Source: Marijn Haverbeke, https://eloquentjavascript.net/01_values.html
Creative Commons License This work is licensed under a Creative Commons Attribution-NonCommercial 3.0 License.