Basic syntax for JavaScript

Variable

1). Understanding: A variable is an identification of the memory used to store variable data

2). Definition: Defined by var

var i = 1;alert (i); i = "abc"; alert (i);

Data type 1). Type classification of data:

L Basic Type: numeric (number), String, Boolean (Boolean), undefined

L Object types: Objects (object), arrays (array), functions (function)

2). The type of the variable:

L Basic Type: variable that holds basic type data

L Reference type: A variable that holds the address value of the object type data

The reference type, just the address where the data is saved.

3). Detailed: Basic type data

A. Numeric type (number)

Integers and decimals

Infinity

NaN

B. String types (String)

Definition: The data "HelloWorld" ' HelloWorld ' of a pair of single quotes or double-quoted packets

C. Boolean value type (Boolean)

Only true and false two kinds of values

D.undefined type (differs from "undefined")

Its value is ' undefined ', if the variable is not assigned, i.e. its value is undefined

var u; Undefined (not initialized or undefined) alert (typeof i);

4). Introduction: Object type data

A. Object: A collection of properties, that is, a hash list of key values

B. Array: Ordered list

C. Function: Object data that contains executable code

5).conversions between data types:

A. String of basic type String---> Object type

str = "123"; str = Str/1;//alert (typeof str);//number automatically converted to base type values

B. Numeric string--->number

str = "123"; str = str + 1; is a connector//alert (str); "1231"

C. Any type of--->boolean type

1. Data that can be automatically converted to false: empty string, null, undefined, 0,nan

2. All others are true

</pre><p align= "left" ><pre name= "code" class= "javascript" >STR = "123"; str = Str/1;//alert (typeof str );//number automatically converts to the basic type value str = "123"; str = str + 1; is a connector//alert (str); "1231" str = str * 1;//1231STR = str + 1;//1232 is an arithmetic operator//alert (str); str = null;if (!str) {//alert ("----1");} str = "a"; if (str) {//alert ("----2");} str = 0;if (!str) {//alert ("----3");} str = undefined;if (!str) {//alert ("----4");}

Operator (Special)

1). Parentheses: () to define or invoke a function

2). Bracket operator: [] used to create an array/get array elements

3). Curly brace operator: {} used to create an object

4). Colon operator: Colon is used to separate the property name and property value of an object

5). typeof: The string that corresponds to the data type used to get the variable

6). instanceof: Determines whether an object is of the specified type

7). Delete: Delete the specified data

Use of functions

1). function

function sum (n, m) {

return n + m;

}
2). var + function

var sum2 = function(n, m) {

return n + m;

};

Parameter problems with functions

L arguments can not be inconsistent with formal parameters

L can dynamically obtain real parameters in a function.

L Arguments: There is a built-in reference variable in each function that points to an array of all the arguments that represent the call to simultaneous

var sum4 = function() {

var result = 0;

for (var i = 0; I <arguments.length; i++) {

result+= Arguments[i];

}

return result;

}

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Basic syntax for JavaScript