Javascript core objects: 1. Math object; 2. Number object; 2. Boolean object; 4. String object; 5. Array object; 6. Date object; 7. Object object; 8. Function object; 9. RegExp object.
The operating environment of this tutorial: windows7 system, javascript version 1.8.5, Dell G3 computer.
Core objects of javascript
1. Math object
The Math object is used to perform mathematics The operation does not use new to create an instance, but directly uses Math to directly call its properties and methods. For example
var pi_value=Math.PI
var sprt_value=Math.sprt(16);
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Math object properties
Properties
Description
E
Returns the base e of natural numbers (approximately equal to 2.718)
LN2
Returns the natural logarithm of 2 (approximately equal to 0.693)
LN10
Returns the natural logarithm of 10 (approximately equal to 2.302)
LOG2E
Returns the base 2 pair of e Number (approximately equal to 1.414)
LOG10E
Returns the base 10 logarithm of e (approximately equal to 0.434)
PI
Returns pi (approximately equal to 3.14159)
SQRT1_2
Returns the reciprocal of the square root of 2 (approximately equal to 0.707)
SQRT2
Returns the square root of 2 (approximately equal to 1.414)
Math object method
Method
Description
abs(x)
Returns the absolute value of parameter x
acos(x)
Returns the inverse cosine function of parameter x
asin(x)
Returns parameter x The arcsine value of
atan(x)
returns the parameter x as a value between -PI/2 and PI/2 radians The arcsine function
atan2(y,x)
returns the angle from the x-axis to the point (x, y) (between -PI/2 and PI /2 radians)
ceil(x)
Round up the parameter x. For example, the value of Math.ceil(2.3) is 3
cos(x)
Returns the cosine value of parameter x
exp(x)
Returns the exponent of e
floor
Round the parameters down. For example, the value of Math.ceil(2.3) is 2
##log ( x)
Returns the natural logarithm of the parameter x (base is e)
max (x, y)
Returns the two Maximum number
min(x,y)
Returns the minimum of two numbers
pow(x, y)
Returns the y power of parameter x
random()
Returns a random number between 0~1
round(x)
Round parameter x
sin(x)
Return the sine value of parameter x
sqrt(x)
Returns the square root of parameter x
tan(x)
Returns parameter Tangent
2. Number object
var num1=new Nunber(value);
var num2=Nunber(value);
var num3=123;
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Number’s object property
Attribute
Description
MAX_VALUE
The maximum number that JavaScript can represent
MIN_VALUE
JavaScript can represent the smallest number
NaN
non-numeric value
NEGATIVE_INFINITY
Represents negative infinity -Infinity, this value is returned when overflows
POSITIVE_INFINITY
Represents positive infinity nfinity, this value is returned when overflows
Object method of Number
Method
Description
toString()
Convert the value into a string, use IRadix to specify the base, the default is decimal
toFixed(x)
Convert the value into a character String, the number with x digits after the decimal place of the result
toExponential(x)
Convert the object value into exponential notation, the result There are numbers x after the decimal point
toPrecosion(x)
Format the value into the length given by parameter
##valueOf
Returns the original value of a Number object
3、Boolean对象
var b=new Boolean(value);
var b=false;
参数只有false、0、null、undefined的情况下会得到false的对象，否则会得到值为true
var arrObj=new Array();
var arrObj=new Array(size);
var arrObj=new Array(element0,element2);
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（2）数组的length属性
（3）Array对象的方法
Array对象的方法
方法
描述
push()
向数组末尾添加一个或者更多元素，并返回新的数组长度
unshift()
向数组的开头添加一个或者更多元素，并返回新的数组长度
pop()
删除并返回数组的最后一个元素
shift()
删除并返回数组的第一个元素
splice()
删除元素并向数组添加新的元素
sort()
对数组元素进行排序
reverse()
颠倒数组中元素的顺序
toString()
把数组转换成字符串
join()
把数组的所有元素放到字符串中并用指定的分隔符进行分离
concat()
连接两个或者更多的数组，并返回结果
slice()
从某个已有的数组返回选定的元素
（4）二维数组的定义与访问
var citye=new Array();
citye[0]=new Array{"sha","上海","SHANGHAI","SH"};
citye[1]=new Array{"HYN","黄岩","HUANGYAN","HY"};
citye为二维数组，使用“数组变量名[子数组索引号][子数组中元素的索引号]”的格式来访问
遍历为双层循环遍历
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6、Date对象
（1）Date对象的创建
var dateObj1=new Date();
var dateObj2=new Date(dateval);
var dateObj3=new Date(year,month,date);
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（2）Date对象的方法
var d3 =new Date("2019-12-12");
d3.getDate(); //获取当前日期中的日12
d3.getMonth(); //获取月份返回11，月份为（1-11）
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7、Object对象
（1）对象的创建
方式一：
var cat1=new Object();
cat1.name="猫咪";
cat2.color="黄色";
cat.eat()=function(){
alert(this.name+"吃老鼠");
};
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方式二：
var cat1=new ();
cat1.name="猫咪";
cat2.color="黄色";
cat.eat()=function(){
alert(this.name+"吃老鼠");
};
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方式三：
var cat1={
cat1.name="猫咪";
cat2.color="黄色";
cat.eat()=function(){
alert(this.name+"吃老鼠");
};
}
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创建对象实例
var cat2=Object.create(cat1);
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8、Function对象
（1）function的创建
funcation sum(x,y){
return (x+y);
}
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（2）第二种格式
function Cat(name,color){
cat1.name=name;
cat2.color=color;
cat.eat()=function(){
alert(this.name+"吃老鼠");
};
}
var cat1= new Cat("猫咪","黄色");
cat1.eat();
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9、RegExp对象
(1)创建RegExp对象
var regObj=new RegExp("pattern"[,flags])
var regObj=/pattern/{flags}
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