Javascript - Introduction Javascript Syntax

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Case-sensitivity

In Javascript everything is case-sensitive; variables, function names, and operators are all case-sensitive.

A variable named test is different from a variable named Test.

typeof can't be the name of a function, because it's a keyword; however, typeOf is a valid function name.

Identifiers

An identifier is the name of a variable, function, property, or function argument.

Identifiers may be one or more characters in the following format:

  • The first character must be a letter, an underscore (_), or a dollar sign ($).
  • All other characters may be letters, underscores, dollar signs, or numbers.

Letters in an identifier may include extended ASCII or Unicode letter characters, though this is not recommended.

Javascript identifiers use camel case, meaning that the first letter is lowercase and each additional word is offset by a capital letter, like this: 

firstSecond 
myCar 
doSomethingImportant

Keywords, reserved words, true, false, and null cannot be used as identifiers.