JavaScript Basics-variable-operator-flow control statements

JavaScript composition

A complete JavaScript implementation is made up of the following 3 different parts:

ECMAScript: Describes the grammar and basic objects of the language;

The Document Object model, or DOM, is a description of the methods and interfaces for handling Web page content;

Browser object models (Browser object model, BOM): Describes the methods and interfaces that interact with the browser.

Variable

Variable type: Object String function Boolean undefined null number

JavaScript is a weak type, declaring a variable cannot declare a data type: int i=0;

can only be i=0 by VAR; declaring variables, unlike var in C #, is not a type inference in C #

JS is a dynamic type, so var i=0;i= "ABC"; it's legal.

Determining variable Initialization

The true and False in JS

True: true, not 0 digits, non-empty string, non-empty object

False: False, number 0, empty string, empty object, undefined

var a=false or a=0 or a=null or a=undefined or a= '

if (a) false

Operator

Programming languages are basically the same, listing Special:

1. = = =,! ===

A==b first converts the type, then compares, A===b does not convert the type, directly than

var a = 1;

var B = "1";

Alert (A = = B); True

Alert (A = = B); False

2 | | Returns the first value that is not false (the object can also), or the last value if all is false, the returned result is not necessarily a Boolean value

var a=2;

var b=0;

var c=b| | A

Window.alert (c); Output 2

Process Control Statements

Determine if else, switch case

Loop while (does while) for

JS does not have a foreach but can be used like a foreach

for (var item in data)

{

alert (item);

}

Jump out of break, continue

JavaScript Basics-variable-operator-flow control statements