A, JavaScript variables
In JavaScript to create variables are often referred to as "declaration" variable.
Using the var keyword to declare variables.
Note:
1, the variable must begin with a letter
2, the variable can begin with $ and _ symbols (though we do not recommend it)
3, variable names are case sensitive (y and Y are different variables)
4, and JavaScript statements JavaScript variables are case-sensitive.
Example:
<Script type = " text / JavaScript " > // global variable name = ' Seven ' ; // defined function function FUNC () { // local variable var Age = 18 is ; // global variable Gender = " M " } </ script>
Two, JavaScript data type
data type is classified into JavaScript object types and primitive types:
1, primitive types:
numeric (Number The)
JavaScript only a digital type. Decimal point numbers can also be used without:
var = 34.00 X1; // use decimal write
var x2 = 34; // do not use to write decimal
Number object-related attributes
Number.MAX_VALUE maximum value
minimum value Number.MIN_VALUE
Number.NaN special non-numeric value
Number.NEGATIVE_INFINITY negative infinity
Number.POSITIVE_INFINITY positive infinity
Number.toExponential () by exponential notation format numbers
Number.toFixed () using the fixed-point notation format numbers
Number.toLocaleString () format digital conversion costs string
Number.toPrecision () format numbers valid bit
Number.toString () to - digital converted to a string
Number.valueOf () returns the original value
string (string)
string can be any text enclosed in quotation marks. You can use single or double quotes:
var carname = "Volvo XC60"; // double quotes
var carname = 'Volvo XC60'; // single quotes
String object attributes related
to String.charAt () Returns a string of n characters
of String.charCodeAt () Returns a string code of n characters
String.concat () connection string
the String.fromCharCode () created from a character code - string
String.indexOf () to retrieve a string
String.lastIndexOf () to retrieve a string from back to front
String.length string length
String.localeCompare () with a specific local order to compare two strings
String.match () match is found or a plurality of regular expressions
String.replace () is a replacement match the regular expression substring
String.search () retrieves the regular expression match substrings
String.slice () extracting a substring
the String.split () dividing the string into a string array
of String.substr () extracting a substring
string .substring () returns a string substring
String.toLocaleLowerCase () to convert a string lowercase
String.toLocaleUpperCase () to convert the string to uppercase
String.toLowerCase () to convert the string to lowercase
String.toString () Returns a string
the String.toUpperCase () the string into uppercase
String.valueOf () returns a string
Boolean (Boolean)
Boolean (logical) can have only two values: true or false.
to true X = var;
var Y = to false;
Boolean object-related attributes
Boolean.toString () converts the character string into a Boolean value
Boolean.valueOf () Boolean Boolean object
2, object types:
an array (the Array)
var = new new cars the Array ();
cars [0] = "Saab";
cars [. 1] = "Volvo";
cars [2] = "the BMW";
or
var cars = new Array ( "Saab ", "Volvo", "BMW");
Array对象相关属性
Array.concat( ) 连接数组
Array.join( ) 将数组元素连接起来以构建一个字符串
Array.length 数组的大小
Array.pop( ) 删除并返回数组的最后一个元素
Array.push( ) 给数组添加元素
Array.reverse( ) 颠倒数组中元素的顺序
Array.shift( ) 将元素移出数组
Array.slice( ) 返回数组的一部分
Array.sort( ) 对数组元素进行排序
Array.splice( ) 插入、删除或替换数组的元素
Array.toLocaleString( ) 把数组转换成局部字符串
Array.toString( ) 将数组转换成一个字符串
Array.unshift( ) 在数组头部插入一个元素
对象(Object)
对象由花括号分隔。在括号内部,对象的属性以名称和值对的形式 (name : value) 来定义。属性由逗号分隔:
var person={firstname:"John", lastname:"Doe", id:5566};
或者
var person={
firstname : "John",
lastname : "Doe",
id : 5566
};
Object对象相关属性
Object.constructor 对象的构造函数
Object.hasOwnProperty( ) 检查属性是否被继承
Object.isPrototypeOf( ) 一个对象是否是另一个对象的原型
Object.propertyIsEnumerable( ) 是否可以通过for/in循环看到属性
Object.toLocaleString( ) 返回对象的本地字符串表示
Object.toString( ) 定义一个对象的字符串表示
Object.valueOf( ) 指定对象的原始值
空(null)
null是JavaScript语言的关键字,它表示一个特殊值,常用来描述“空值”。
未定义(Undefined)
undfined是一个特殊值,表示变量未定义。
三、JavaScript函数
3.1、函数语法:
函数就是包裹在花括号中的代码块,前面使用了关键词 function:
function 函数名(){
执行代码
}
3.2、函数的分类
// 普通函数 function func() { return "yusheng_liang" } // 匿名函数 var func = function(arg){ return "yusheng_liang"; }; // 自执行函数 (function(arg){ console.log(arg); })('123')
3.3、调用带参数的函数
在调用函数时,您可以向其传递值,这些值被称为参数。这些参数可以在函数中使用。您可以发送任意多的参数,由逗号 (,) 分隔:
语法:
function myFunction(var1,var2){
代码
}
示例:
<button onclick="myFunction('Harry Potter','Wizard')">Try it</button> <script> function myFunction(name,job) { alert("Welcome " + name + ", the " + job); } </script>
3.4、带有返回值的函数
有时,我们会希望函数将值返回调用它的地方。通过使用 return 语句就可以实现。在使用 return 语句时,函数会停止执行,并返回指定的值。
语法:
function myFunction(){
var x=5;
return x;
}