Summary

  • Dynamic typing, meaning that there exist data types, but variables are not bound to any of them. A union is a special data type available in programming language C that allows storing different data types in the same memory location and dynamic typing is often implemented using tagged union.

  • The Number type represents both integer and floating point numbers. Besides regular numbers, there are special numeric values like Infinity, -Infinity, and NaN.

  • The BigInt type was recently added to the language to represent integers of arbitrary length. It is useful when we are doing stuff like cryptography or microsecond-precision timestamps. A BigInt can be created by appending n to the end of an integer.

  • A String type has to be surrounded by quotes. Double and single quotes are simple quotes while backticks are extended functionality quotes that allow variable and expression embedding using ${...}.

  • The Boolean type has only two values, true and false.

  • The null type is a special one represents unknown value. It is not a reference to a non-existing object or a null pointer.

  • The undefined type means the variable is declared but not assigned. Technically it is possible to explicitly assign undefined to a variable but it is note recommended. Normally, one uses null to assign an empty or unknown value to a variable, while undefined is reserved as a default initial value for unassigned things.

  • The Object type is used to store collections of data and more complex entities compared with every other type which is primitive and stores only one single thing.

  • The Symbol type is used to create unique identifiers for objects.

  • The typeof operator returns the type of the operand.

  • The result of typeof Math is object as Math is a built-in object that provides mathematical operations.

  • The result of typeof null is object. That’s an officially recognized error, coming from very early days of JavaScript and kept for compatibility. `null is a special value with a separate type of its own.

  • The result of typeof alert is function. function belongs to the object type, so what typeof shows is incorrect, but can be convenient in practice.

  • typeof(x) is the same as typeof x. typeof is an operator, not a function. The parentheses here aren’t a part of typeof but a kind of mathematical grouping for expression.

Tasks

  • String quotes

    let name = "Ilya"
alert(`hello ${1}`)
// hello 1
alert(`hello ${"name"}`)
// hello name
alert(`hello ${name}`)
// hello Ilya

References