What is a String object
String object: an object used to process text strings
String object creation
Create a string in a literal way.
字面量的方式创建字符串 var str1="world"; console.log(str1);
Constructor creates a string
var str=new String("hellow"); console.log(str);
Method usage of String object
The charAt() method returns the specified character from a string.
var str = "Brave new world";
console.log(str.charAt(0));//B
console.log(str.charAt(1));//r
console.log(str.charAt(2));//a
console.log(str.charAt(3));//v
console.log(str.charAt(4));//e
console.log(str.charAt(999));//
The concat() method concatenates one or more strings with the original string to form a new string and returns.
var str = "Hello, ";
console.log(str.concat(" have a nice day.")); //Hello, have a nice day.
search() Get the first occurrence of a character or string fragment
var str='hello world!';
console.log(str.search('e'));//1
console.log(str.search('a'));//-1 没找到则返回-1
match() matches a character or string that meets the conditions and returns an array
var str='hello world!';
console.log(str.match('l'));//以数组的形式返回
console.log(str.match('a'));//null
replace() replace
var str='hello world!';
//replace(参数1,参数2); 参数1：替换谁 参数2：替换值
console.log(str.replace('l','哈哈'));// he哈哈lo world!
split() string cutting, return array after cutting
/*split(参数1,参数2)
参数1 ：必需。字符串或正则表达式，从该参数指定的地方开始切割。
参数2 ：可选。该参数可指定返回的数组的最大长度。如果设置了该参数，返回的子串不会多于这个参数指定 的数组。
如果没有设置该参数，整个字符串都会被分割，不考虑它的长度。*/
var str='good morning';
console.log(str.split());//["good moronioong"]
console.log(str.split(''));//["g", "o", "o", "d", " ", "m", "o", "r", "n", "i", "n", "g"]
console.log(str.split(' '));//["good", "morning"]
console.log(str.split('n'));//["good mor", "i", "g"]
console.log(str.split('n',2));//["good mor", "i"]
slice (start position, end position) Get the string fragment between two index values
var str='abcdefg';
console.log(str.slice(2,4));//cd 从下标2开始截取，到下标4结束，但不包含4
substr (start position, the length of the interception to obtain the string fragment between the two index values
var str='abcdefg';
console.log(str.substr(2,3));//cde 从下标2开始截取，截取长度为3的字符串长度
indexOf() Get the first occurrence of a character or string, return the index value if found, return -1 if not found
var str = 'hello world';
console.log(str.indexOf('o'));//4
console.log(str.indexOf('p'));//-1
toLowerCase() converts the string to lowercase
var str='Hellow World';
console.log(str.toLowerCase());//hellow world
toUpperCase() converts the string to uppercase
var str='Hellow World';
console.log(str.toUpperCase());//HELLOW WORLD
Find out the number of occurrences of a character in a string
//找出'o'出现的次数
var str = 'good morning';
var num = 0;
for (var i = 0; i < str.length; i++) {
if (str.charAt(i) == 'o') {
num++;
}
}
console.log(num); //3
String output in reverse order
var str='good morning';
console.log(str.split('').reverse().join(''))//gninrom doog
What is a Math object
The concept of the
Math object The function of the Math (arithmetic) object is to perform common arithmetic tasks.
Method use of Math object
max(x,y,z…) 返回 x y z …中的最大值。
min(x,y,z…) 返回 x y z …中的最小值。
ceil(x) round up
console.log(Math.ceil(5.2));//6
console.log(Math.ceil(5.5));//6
console.log(Math.ceil(5.8));//6
floor(x) rounded down
console.log(Math.floor(5.2));//5
console.log(Math.floor(5.5));//5
console.log(Math.floor(5.8));//5
round(x) rounding
console.log(Math.round(5.2));//5
console.log(Math.round(5.5));//6
console.log(Math.round(5.8));//6
random() returns a random number between 0 and 1, including 0 but not 1
//随机生成0~1之间的随机数（包括0，但不包括1）
console.log(Math.random());
//随机生成0~100之间的随机数(包括0，不包括100)
console.log(Math.random()*100);
//随机生成5~10之间的随机数
console.log(Math.random()*5+5);
//随机生成5~10之间的整数
console.log(Math.floor(Math.random()*5+5));
Case: Randomly generate an integer within 100, put it into an array, cannot repeat, sort in ascending order
var arr = [];
for (var i = 0; i < 100; i++) {
var num = Math.floor(Math.random() * 100); // 随机生成100个数字
if (arr.indexOf(num) == -1) {
// 如果不重复的情况，则存入arr中
arr.push(num);
}
}
console.log(arr);
arr.sort(function (a, b) {
//小到大排列
return a - b;
});
console.log(arr);