@description = "This lesson is a whirlwind tour of JavaScript features for people already fluent in another programming language. For a more measured and beginner-focused tutorial, start at the top of this Learn to Code with JavaScript track instead."
"In JavaScript, there is a beautiful, elegant, highly expressive language that is buried under a steaming pile of good intentions and blunders." - Douglas Crockford, JavaScript: The Good Parts
JavaScript has seven data types; six are called primitives:
BooleanNullUndefinedNumberStringSymbol (new in ECMAScript 6)Object (sometimes called "hash") comprises all other types, including
RegExpFunctionDateMapuser.name
user['name']
The normal way:
for (var i = 0; i<a.length; ++i) { ... }
In old JavaScript implementations, the above suffers from a performance problem, so you may see the following recommended instead:
for (var i = 0, n = a.length; i<n; ++i) { ... }
== performs type coercion
2 == [2] // true
The above evaluates as if it were expanded thus:
2 === Number([2].valueOf().toString())
see also Why does 2 == [2] in JavaScript?
"" == "0" // false
0 == "" // true
0 == "0" // true
false == "false" // false
false == "0" // true
false == undefined // false
false == null // false
null == undefined // true
" \t\r\n" == 0 // true
(from http://bonsaiden.github.com/JavaScript-Garden/#types.equality)
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