javascript - what is differeces between var a = b = 2 and var a = 2; var b=2; -

when declare variable in function, face problem.

var b = 44; function test(){     var = b = 2; } 

but works fine:

 var b = 44;  function test(){     var a;     var b = 2;  } 

variable b on rides global b variable.

i cannot find documentation behavior.

is there documentation ?

demo : http://jsfiddle.net/uq4nxk1k/1/

i don't know can find documentation, here's explanation result obtained :

local > global

when declare global variable, it's available anywhere in file. inside "test()", when write :

var = b = 2; 

you creating new variable a, take value of global variable b , changing, @ same time, value of b 2 -> overriding value.

when write (inside test()) :

var a, b;  

or

var a;  var b; 

you're declaring 2 more variables, known inside function and, local > global, if write b = 2, can face 2 situations :

1. if console.log(b) inside test(), obtain 2
2. if console.log(b) outside test(), obtain 44

declaration != assignment

very important ->

• var a, b; is declaration

• a = b = 25; is assignment (i'd double assignment)

• var = b = 25 is declaration , assignment @ same time.

i hope helps!!!:) tell me if unclear or if need other explanation.