Module 5: JavaScript in Browser D. Petin 07/2014

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object will be created.

You can take it if you

need. In W3C browsers this object will be passed as a first parameter of event handler:

btn.addEventListener(“click”, action, false);

Where action was defined as:

function action (e) { . . . }

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located in object window and its name is event:
var e

= window.event;

You have a possibility to use a cross-browser solution.:

function action (e) {
e = e || window.event;
. . .
}

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includes some additional behavior: bubbling and capturing or displaying context

menu.

If you don't need a default behavior, you can cancel it. Use object event and next methods for this purpose:

e.preventDefault();

e.stopPropagation();

for discarding bubbling and capturing.

for aborting default browser behavior.
.

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variable in JavaScript.

Sandbox is a special part of memory that

will be managed by browser: JavaScript takes simplified and secure access to "memory“, browser translates JS commands and does all low-level work.

As a result memory, PC and user data has protection from downloaded JavaScript malware.

by browser in the sandbox and used for storing variables.

Each

function in JavaScript has its own personal scope. Scope is formed when a function is called and destroyed after the function finishes.

This behavior helps to manage local variables mechanism.

window object is a top-level scope for all default and global variables.

10,
b: 20
};
test_scope = {
b:

40
};

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var a = 10;
test();
function test () {
a = 30;
var b = 40;
}
var b = 20;
console.log(a, b);

For example string or function. There is simple division into

value-types and reference-types for this reason.

Value-types are stored in scope completely and for reference-types only reference to their location is put in scope. They themselves are located in place called "memory heap".

String and all Objects are reference-types. Other data types are stored in scope.

finished, scope should be destroyed and as a result all

local variables should be destroyed.

This will work for value-types.

As for reference-types: deleting the scope destroys only reference. The object in heap itself will be destroyed only when it becomes unreachable.

referenced from the client area of code.

Garbage collector is responsible

for the cleanup of unreachable objects.

It's a special utility that will launch automatically if there isn’t enough space in the sandbox.

If an object has at least one reference it is still reachable and will survive after memory cleaning.

b: reference
};
… somewhere in heap …
function action () {

var a = new Point(10, 20),
b = new Point(15, 50);
}

{x: 10, y: 20}

{x: 15, y: 50}

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deleted it is still reachable, isn't it?

Absolutely! This mechanism is

called closure.

If you save at least one reference to scope, all its content will survive after function finishing.

return function () {

return value; };
}

var pi = getPi();
. . .
L = 2*pi()*R;

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