Javascript wrinkles

Notes for people who think console.log() is inherently interesting.

Javascript notes and quirks

The plus operator: +
strings containing numbers work in calculations if prefixed with a + sign e.g. add these: +"1.1" + +"1.1".
Check existence
var myArray = new Array(); if (!myArray[0]) {console.log("Not defined")} uses false to print the statement.
Variable scope
local to the code a block resides within (not block statement scope). They are also 'hoisted' as if at the top of a function/statement.
Try this function Scope() { if (true) { var x = 5 }; alert("x: " + x + ", y: " + y); }; var y = 6;
Declared with the const keyword, e.g. const prefix = '212';z = prefix + 424;alert(prefix);.
Constants cannot share a name with a function or variable in the same scope, or be called directly e.g. alert(prefix);.
Array literals (literals have fixed values) use square brackets: var mynums = ["one", "two", "three"]; alert(mynums[0]).
Avoid spaces after \ in multiline string literals
Always add a return immediately after \ as '\ ' will produce an error. This multiline string is broken before 'another'.
Return the entire code for a function
Simply omit the brackets alert(IsDefined)
Retrieving values from an object
value by dot notation: flight.departure.IATA
value by name: flight['number'] (Douglas Crockford: Javascript: the Good Parts, or the video or a series)
value of array element in object: employees.accounting[1].firstName (from Mastering JSON)
Using the file api
HTML5 allows interaction with local files via its File API specification - test your browser's file api here.

Javascript good practice

Don't use ++ or --
Use += and -= instead, as ++ and -- are too tight, too tricky, too cryptic (Crockford)
Use === and !== for comparison
This will ensure that: 0, '', undefined, null, false, true all return the expected result. Both == and != do type coercion before comparing. This causes \f\r\n\t == 0 to be true. If you want this, use the shorthand (foo) and (!foo) instead of (foo != 0) and (foo == 0) (Crockford)
Avoid using new
Don't use new to create a Boolean, Number or String; and use {} and [] to create a new Object or Array
Use object.create, but not for arrays
because object produced will inherit the array’s values and methods, but lack the length property.
Declare functions before you call them
and declare variables at the top of functions, avoiding for(var i...
Name constructor functions with an initial capital
to help spot instances where they're called without new. Better: use object.create (instead of new) for a new instance of a specific object.