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

Содержание

5. Examplevar a = 2;var b = 2;console.log(a + b);
6. Recap of the previous lecture
7. Scope in ES3 World
8. The Scope of a VariableThe scope of
9. Scope - is a logical boundaries in
10. Scope - is a logical boundaries in
11. Scope can be nested function f() {
12. Nested Scopefunction f() { var x
13. Shadowingvar scope = "global ";
14. Shadowingvar scope = "global ";
15. Shadowingvar scope = "global ";
16. function X() { var a = 3, b
17. HoistingJavaScript hoists all variable declarations, it moves them to the beginning of their direct scopes.
18. Hoistingfoo(); // undefined ("foo" and "bar" exist)function
19. Hoistingvar scope = "global ";function f( )
20. Only functions introduce new scopesNo block scopefunction
21. function test(o) { var
22. var foo = 1;function bar() { if (!foo) { var foo = 10; } alert(foo);}bar();Hoisting
23. Code in global scope Untitled Pagevar
24. Global namespaceEvery variable is global unless it's
25. Global object (WAT)function f(){ x
26. window vs global(function (glob) { // glob
27. Global variables are evilThey are less robust,
28. Globals// antipatternfunction sum(x, y) {// implied globalresult
29. if (("a" in window) == false) { var a = 1; }alert(a);
30. Working with globalwindow.fooif (window.foo) { … }if
31. Namespacesif (window.myNamespace == null){ window.myNamespace = {}; }window.myNamespace.myFunction = function(/* params*/ ) { /* code here */ };
32. immediately invoked function expression in next lecture
33. Скачать презентацию
34. Похожие презентации

Examplevar a = 2;var b = 2;console.log(a + b);

Examplevar a = 2;var b = 2;console.log(a + b);

The Scope of a VariableThe scope of a variable are the locations

Scope - is a logical boundaries in which a variable (or expression)

Scope can be nested function f() { var x = 2;

Nested Scopefunction f() { var x = 2; function

function X() { var a = 3, b = 5; function foo () { var

HoistingJavaScript hoists all variable declarations, it moves them to the beginning of their direct scopes.

var foo = 1;function bar() { if (!foo) { var foo = 10; } alert(foo);}bar();Hoisting

Code in global scope Untitled Pagevar a = 5;var b =

Global namespaceEvery variable is global unless it's in a function and is

Global object (WAT)function f(){ x = “global variable”; // var

window vs global(function (glob) { // glob points to global object }(typeof

Global variables are evilThey are less robust, behave less predictably, and are

Globals// antipatternfunction sum(x, y) {// implied globalresult = x + y;return result;}//

Working with globalwindow.fooif (window.foo) { … }if (“foo” in window) { …

Namespacesif (window.myNamespace == null){ window.myNamespace = {}; }window.myNamespace.myFunction = function(/* params*/ ) { /* code here */ };

immediately invoked function expression in next lecture

REFERENCES JavaScript: The Definitive Guide, Six Editionby David Flanagan Speaking JavaScript: An

Слайды презентации

Слайд 5 Example
var a = 2;
var b = 2;
console.log(a +

Слайд 6 Recap of the previous lecture

Слайд 7 Scope in ES3 World

Слайд 8 The Scope of a Variable
The scope of a

The Scope of a VariableThe scope of a variable are the

variable are the locations
where it is accessible.

For

example:

function foo() {
var x;
}

Слайд 9
Scope - is a logical boundaries in which

Scope - is a logical boundaries in which a variable (or

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

a global variable, a local variable, etc, which generally reflects a logical range of a variable lifetime.

Слайд 10
Scope - is a logical boundaries in which

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

a global variable, a local variable, etc, which generally reflects a logical range of a variable lifetime.

Слайд 11 Scope can be nested
function f() {

var x = 2;
function g() {

var y = 3;
alert(x + y);
}
}

Слайд 12 Nested Scope
function f() {
var x =

2;
function g() {

var y = 3;
alert(x + y);
}
}

inner scope

outer scope

Слайд 13 Shadowing
var scope = "global ";

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

“outer”; // A outer variable
function inner() {
var scope = “inner";
document.write(scope); // Prints "inner"
}
inner();
}
outer();

Слайд 14 Shadowing
var scope = "global ";

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

“outer”; // A outer variable
function inner() {
document.write(scope); // Prints "outer"
}
inner();
}
outer();

Слайд 15 Shadowing
var scope = "global ";

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

// Prints "global"
}
inner();
}
outer();

Слайд 16 function X() {
var a = 3, b =

function X() { var a = 3, b = 5; function foo ()

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

11;
a += b + c;
};
foo();
alert("a = " + a + "; b = " + b);
}
X();

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

Слайд 17 Hoisting
JavaScript hoists all variable declarations, it moves them to the

beginning of their direct scopes.

Слайд 18 Hoisting
foo(); // undefined ("foo" and "bar" exist)

function foo()

{
alert(bar);
}

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

var bar;

foo();

// undefined

Слайд 19 Hoisting
var scope = "global ";
function f( ) {

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

= "global ";
function f( ) {
var scope;
alert(scope);
scope = "local";
alert(scope);
}
f( );

Слайд 20 Only functions introduce new scopes
No block scope
function f()

{
{ // block starts

var foo = 4;
} // block ends
console.log(foo); // 4
}

Слайд 21 function test(o) {
var i

= 0; // i is defined

throughout function
if (typeof o == "object") {
var j = 0; // j is defined everywhere, not just block

for(var k=0; k < 10; k++) { // k is defined everywhere, not just loop
document.write(k);
}

document.write(k); // k is still defined: prints 10
}
document.write(j); // j is defined, but may not be initialized
}

No block scope!