Презентация на тему Scope in ES3 world. (Lecture 3)

variable are the locations
where it is accessible.

For

a variable (or expression) has its meaning. For example,

a variable (or expression) has its meaning.
For example,

var x = 2;
function g() {

2;
function g() {

inner scope

outer scope

// A global variable
function outer() {
var scope =

// A global variable
function outer() {
var scope =

// A global variable
function outer() {
function inner() {
document.write(scope);

5;
function foo () {
var b = 7, c =

var x = function(){
alert(x.toString());
}
x();

beginning of their direct scopes. 

{
alert(bar);
}

var bar;
function foo() {
alert(bar);
}

var bar;


foo();

alert(scope);
var scope = "local";
alert(scope);
}
f( );
var scope

{
{ // block starts

= 0; // i is defined

No block scope!

foo = 10;
}
alert(foo);
}

bar();
Hoisting

type="text/javascript" src="/script.js">




var a = 5;
var b = 2;

function

Index.html

a function and is declared with var
function f(){

“global variable”; // var is missed
}
f();
this.x === “global variable”;
window.x

to global object
}(typeof window !== 'undefined' ? window

less predictably, and are less reusable.
Name clashes. Your code,

x + y;
return result;
}


// antipattern
function foo() {
var a =

var a = 1;
}
alert(a);

in window) { … }
if (typeof “foo” !== “undefined”)

function(/* params*/ ) {
/* code here */
};