Concept: It is a collection of several data put together in a certain order, which is called an "array" as a whole. An array is an ordered collection of data.
Definition form:
<span>var</span> arr1 = <span>new</span> Array(<span>1</span>, <span>5</span>, <span>8</span>, <span>7</span>, <span>2</span>, <span>10</span>); <span>//</span><span>定义了一个数组，其中具有6个数据</span>
<span>var</span> arr2 = <span>new</span> Array(); <span>//</span><span>只是单纯地定义了一个数组（名），但没有给值（数据），即现在是空的</span>
<span>var</span> arr3 = [<span>1</span>, <span>5</span>, <span>8</span>, <span>7</span>, <span>2</span>, <span>10</span>]; <span>//</span><span>同arr1，只是一种简写的定义法。</span>
<span>var</span> arr4 = [ ]; <span>//</span><span>同arr2，也是一个空数组。</span>Usage of arrays: The so-called use actually refers to the use of each item of the array.
Value:
<span>var</span> v1 = arr1[<span>0</span>]; <span>//</span><span>取得数组arr1中的第一项，0叫做下标</span>
<span>var</span> v2 = arr3[<span>3</span>] + <span>10</span>; <span>//</span><span>取得数组arr3中的第4项，4叫做下标</span>
——所谓下标，其实就是数组的每一个数据的“顺序号”——从0开始编号，是连续的整数。Assignment:
arr1[0] = 10;
arr2[<span>0</span>] = <span>22</span><span>;
arr2[</span><span>1</span>] = <span>33.3</span><span>;
arr2[</span><span>2</span>] = “<span>444</span><span>”;
arr2[</span><span>3</span>] =<span> “abc”;
arr2[</span><span>4</span>] = <span>true</span>;//At this time, the array arr2 is equivalent to this: [ 22, 33.3, “444”, “abc”, true ]
The "visual image" of the array (taking arr3 as an example):
下标值： <span>0</span> <span>1</span> <span>2</span> <span>3</span> <span>4</span> <span>5</span><span> 数据值： </span><span>1</span> <span>5</span> <span>8</span> <span>7</span> <span>2</span> <span>10</span>
The syntax to get the length of an array - that is, the number of data in it is:
var v1 = array name.length;
Special note: The maximum subscript of an array is the length of the array minus 1.
Usual pattern for array traversal:
var len = array name.length;
for(var i = 0; i < len; i++)
{
//Here is the processing of each item of the array. The writing method of each item is: Array name[i]
}
Another form of array traversal - for in loop statement.
for( var v1 in array name arr1 )
{
//Here is the loop body, which is a traversal loop specifically for array arr1, where the value of v1 is the subscript value representing each item of the array.
//v1 is just a "temporary variable", representing each subscript, which will change from 0 to the maximum subscript of the array.
}
"two-dimensional" array:
<span>var</span> v1 = [<span>2</span>, <span>5</span>, <span>1</span>, <span>5</span><span>]; </span><span>var</span> v2 = [<span>5</span>, <span>1</span>, <span>6</span>, <span>8</span><span>]; </span><span>var</span> v3 = [<span>8</span>, <span>0</span>, <span>9</span>, <span>7</span><span>]; </span><span>var</span> v4 =<span> [v1, v2, v3]; </span><span>var</span> v5 =<span> [ [</span><span>2</span>, <span>5</span>, <span>1</span>, <span>5</span><span>], [</span><span>5</span>, <span>1</span>, <span>6</span>, <span>8</span><span>], [</span><span>8</span>, <span>0</span>, <span>9</span>, <span>7</span><span>] ]; </span>
——There is actually no difference between v4 and v5. Both of them can be called "two-dimensional arrays".
Operations on "two-dimensional" array elements:
Value:
var s1 = v5[0][1]; //5 //Equivalent to getting the second item of the first item in the array v5 (this is still an array).
var s2 = v5[2][3] + 100; //107
Assignment:
v5[0][1] = 200;
v5[2][3] = 300;
What is a method: A method is actually a function! ——Just if a function "belongs to" an "object", then the function is called a method of the object.
<span>function maibao(){
document.write(“啦啦啦，我是卖报的小行家，卖报啦卖报啦。”);
}
</span><span>var</span> myDreamGirl =<span> {
name: “小花”，
age:</span><span>18</span><span>,
edu：”大学”,
sex:”女”,
nengli1: function (){ document.write(“洗衣！”); } ,
nengli2: function (){ document.write(“做饭！”); } ,
nengli3: maibao
};
</span><span>var</span> v1 = [<span>2</span>, <span>5</span>, <span>1</span>, <span>5</span><span>];
</span><span>var</span> v2 = [<span>5</span>, <span>1</span>, <span>6</span>, <span>8</span>];Strictly speaking, an array is also an object - even strings are objects.
As an object, v1 has properties and methods:
Attributes:
An array.length: indicates the length of the array object
Method:
An array.concat (other array): Connect two arrays to form a new "longer" array.
var s1 = v1.concat( v2
); //At this time, s1 is an array like this: [2, 5, 1, 5, 5, 1, 6, 8];
An array.join("string"): "Concatenate" all the items in the array with the specified characters into a "long" string.
var s2 = v1.join(“//”); //The result s2 is the string “2//5//1//5”
某数组.pop(); //将该数组的最后一项“移除”（删除），并返回该项数据，即该数组少了一项
var s3 = v1.pop(); //结果v1只剩这个：[2,5,1]; s3的值是5
某数组.push(新数据项d1); //将新的数据d1添加到该数组的最后位置，即数组多了一项。
var s4 = v1.push( 55 ); //v1此时为：[2,5,1, 55]， s4的值为新数组的长度，即4
某数组.shift(); //将该数组的第一项“移除”（删除），并返回该项数据，即该数组少了一项
var s5 = v1.shift(); //结果v1只剩这个：[5, 1，55]; s5的值是2
某数组.unshift(新数据项d1); //将新的数据d1添加到该数组的最前位置，即数组多了一项。
var v6 = v1.unshift( 66 ); //v1此时为：[66, 5, 1, 55]， s6的值为新数组的长度，即4
javascript语言是一门基于对象的语言。
<span>var</span> str1 = <span>new</span> String(“abcdefgabc”); <span>//</span><span>这是一个“字符串对象”</span>
<span>var</span> str2 = “abcdefgabc”; <span>//</span><span>这个字符串跟前面str1几乎没有区别</span>
<span>字符串对象的属性：
.length——获得一个字符串的长度（也就是字符个数）
字符串对象的方法：
</span><span>1</span>. str1.charAt( n ); ——获得字符串str1中位置为n的那个字符（字符的位置也是从０开始算起）<span>var</span> s1 = str1.charAt( <span>3</span> ); <span>//</span><span>s1的结果是：”d”</span>
<span>2</span><span>. str1.toUpperCase(); ——获取str1全部转换为大写的结果
</span><span>var</span> s2 = str1.toUpperCase(); <span>//</span><span>s2的结果是：”ABCDEFGABC”</span>
<span>3</span><span>. str1.toLowerCase(); ——获取str1全部转换为小写的结果
</span><span>var</span> s3 = str1.toLowerCase(); <span>//</span><span>s3的结果是：”abcdefgabc”</span>
<span>4</span><span>. str1.replace(“字符1”, “字符2”); ——将str1中的“字符1”替换为“字符2”
</span><span>var</span> s4 = str1.replace(“cd”, “<span>999</span>”); <span>//</span><span>s4的结果是：”ab999efgabc”</span>
<span>5</span>. str1.indexOf(“字符1”); ——获得“字符１”在str1中第一次出现的位置，如果没有出现，结果是-<span>1</span>
<span>var</span> s5 = str1.indexOf(“ab”); <span>//</span><span>s5的结果是0</span>
<span>6</span>. str1.lastIndexOf(““字符1”); ——获得“字符１”在str1中最后一次出现的位置，如果没有出现，结果是-<span>1</span>
<span>var</span> s6 = str1.lastIndexOf(“ab”); <span>//</span><span>s6的结果是7</span>
<span>7</span><span>. str1.substr(n, m ) ——取得str1中从位置n开始的m个字符，m可以省略，则表示从位置n一直取到字符串的最后——注意，这种“取”并不影响str1这个原始字符
</span><span>var</span> s7 = str1.substr(<span>2</span>, <span>4</span>); <span>//</span><span>s7为：”cdef”</span>
<span>8</span><span>. str1.substring( n, m )——取得str1中从位置n到位置m的前一个字符。
</span><span>var</span> s8 = str1.substring(<span>2</span>, <span>4</span>); <span>//</span><span>s8为：”cd”</span>
<span>9</span><span>. str1.split(“字符1”) ——将str1以指定的“字符1”为分界，分割成一个数组，结果是一个数组
</span><span>var</span> s9 = str1.split(“b”); <span>//</span><span>s9的结果是一个数组：[“a”, “cdefga”, “c”]</span>Math对象是一个系统内部定义的对象，我们无需去“新建一个Math对象”——跟string对象和array对象不同。即Math对象是直接使用的。
我们学习Math对象，无非是学习一些常见的数学处理函数——这里当就叫做方法了：
属性：
Math.PI——代表圆周率这个“常数”
方法：
<span>1</span><span>. Math.max(数值1，数值2，…..) ——求得若干个数值中的最大值。
</span><span>2</span><span>. Math.min(数值1，数值2，…..) ——求得若干个数值中的最小值。
</span><span>3</span><span>. Math.abs( 数值1) ——求得数值1的绝对值
</span><span>4</span><span>. Math.pow( x，y) ——求得数值x的y次方，也就是“幂运算”
</span><span>5</span><span>. Math.sqrt( x ) ——求得x的开方
</span><span>6</span><span>. Math.round( x ) ——求得x的四舍五入的结果值；
</span><span>7</span><span>. Math.floor( x ) ——求得x的向下取整的结果，即找到不大于x的一个最大的整数。
a) Math.floor( </span><span>3.1</span> ) <span>3</span><span>
b) Math.floor( </span><span>3.8</span> ) <span>3</span><span>
c) Math.floor( </span><span>3</span> ) <span>3</span><span>
d) Math.floor( </span>-<span>3.1</span> ) -<span>4</span><span>
e) Math.floor( </span>-<span>3.8</span> ) -<span>4</span>
<span>8</span><span>. Math.ceil( x ) ——求得x的向上取整的结果，即找到不小于x的一个最小的整数
a) Math.floor( </span><span>3.1</span> ) <span>4</span><span>
b) Math.floor( </span><span>3.8</span> ) <span>4</span><span>
c) Math.floor( </span><span>3</span> ) <span>3</span><span>
d) Math.floor( </span>-<span>3.1</span> ) -<span>3</span><span>
e) Math.floor( </span>-<span>3.8</span> ) -<span>3</span>
<span>9</span>. Math.random() ——获得一个0~<span>1范围中的随机“小数”，含0，但不含1
</span><span>//</span><span>获得两个整数（n1，n2）之间的随机整数的通用做法：</span>
<span>var</span> v1 =<span> Math.random()
v1 </span>= v1 * (n2-n1+<span>1</span><span>);
v1 </span>= Math.floor( v1 ) + n1; <span>//</span><span>此时v1就是结果
</span><span>//</span><span>将上述3步写出一步就是(通用公式）：</span>
<span>var</span> v1 = Math.floor( Math.random() * (n2-n1+<span>1</span>) ) + n1
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