Brief History of JavaScript

from Wikipedia https://en.wikipedia.org/wiki/JavaScript

JavaScript

JavaScript (/ˈdʒɑːvəˌskrɪpt/),often abbreviated as JS, is a programming language that conforms to the ECMAScript specification.

JavaScript is high-level, often just-in-time compiled, and multi-paradigm. It has curly-bracket syntax, dynamic typing, prototype-based object-orientation, and first-class functions.

Weakly typed

JavaScript is weakly typed, which means certain types are implicitly cast depending on the operation used.

  • The binary + operator casts both operands to a string unless both operands are numbers. This is because the addition operator doubles as a concatenation operator
  • The binary - operator always casts both operands to a number
  • Both unary operators (+, -) always cast the operand to a number

JavaScript includes a number of quirks that have been subject to criticism

left operand operator right operand result
[](empty array) + [](empty array) ""(empty string)
[] (empty array) + {} (empty object) "[object Object]" (string)
false (boolean) + [] (empty array) "false" (string)
"123"(string) + 1 (number) "1231" (string)
"123" (string) - 1 (number) 122 (number) 
('b' + 'a' + +'a' + 'a').toLowerCase(); // "banana"