Common ways to summarize strings, arrays and Math

1. String method
str.charAt() //What is the character at position xx
str.toLowerCase() //Convert all characters to lowercase
str.toUpperCase() // Convert all characters to uppercase characters
str.indexOf() //The position where the xx character first appears
str.laseIndexOf() //The position where the xx character last appears
str.substring() //The string starts from Which position is intercepted to which position, the original array remains unchanged
str.split() //The string is split into an array using xx characters

var arr = 'If you must say yes, say it with an open heart.';
console.log(arr.charAt(3));//yconsole.log(arr.toLowerCase());//if you must say yes, say it with an open heart.console.log(arr.toUpperCase());//IF YOU MUST SAY YES, SAY IT WITH AN OPEN HEART.console.log(arr.indexOf('y'));//3console.log(arr.lastIndexOf('y'));//23console.log(arr.subString(4,10));//ou musconsole.log(arr.split(" "));//["If", "you", "must", "say", "yes,", "say", "it", "with", "an", "open", "heart."]

1. substrng (start starting position index, end ending position index) The intercepted position does not include the end position character, just write one parameter to intercept from the starting position to the end
          var str='abcdefg';  
           str.substring(1) //Get bcdefg str.substring(1,3) //Get bc

When entering a negative value, change the negative value to 0, whichever is smaller is used as the starting position

              str.substing(-1,1)   =>str.substring(0,1) //a
              str.substring(1,-2)  =>str.substring(0,1) //a

2.slice (start starting position index, end ending position index) is basically similar to substring, the difference is that the parameter is a negative number.

Var Str = 'Abcdefg';
## STR.SLICE (1) // Bcdefg Str.substring (1,3) // BC
## Input negative value Add to the length of the string

            str.slice(-1)                                         ’ ’ ’ s ’       use         through ’ through through through through' through ’ through ’s ‐   ‐ ‐‐ ‐‐‐ and ​ to the length of the string. 1,5) // BCDE
Str.slice (-2, -1) = & GT; Str.slice (5,6) // f
Value Absolute value is greater than the length of the string to 0

Str.slice (-22) = & GT; Str.substring (0) // abcdefg
## The second parameter absolute value is greater than the length of the string, returned # 3.substr (start starting position index, end the number of characters to be returned)

var str='abcdefg';

str.substr(1) //bcdefg str.substr( 1,1) //b

When a negative value is entered, the start parameter is added to the length of the string. When end is negative, the parameter becomes 0

str.substr(-1) => str.substr(6)//g                                                                                                                                                                                                                                                          # arr.push() //Add elements after the array, return the array length, and change the original array
arr.unshift() //Add elements in front of the array, return the array length, and change the original array
arr.pop () //Delete the last element of the array, return the last element, and the original array changes
arr.shift() //Delete the first element of the array, return the first element, and the original array changes
arr.join () //Concatenate each element of the array into a string with xx characters, and the original array remains unchanged
arr.splice(start,num,args) //From the start position, replace num elements with args=a , b, c, d, e, the original array changes
arr.reverse() //Reverse the array, the original array changes
arr.concat() //Splice the array, the original array remains unchanged
arr .sort() // Sort from small to large, the original array changes

var arr = [1,2,'three',4,5];var arr1 = ['love',99] ;
console.log(arr.push(6));//6console.log(arr.unshift(0));//7console.log(arr.pop());//6console.log(arr.shift());//0console.log(arr.join('-'));//1-2-three-4-5console.log(arr.splice(2,1,3,4));//["three"]console.log(arr);//[1, 2, 3, 4, 4, 5]console.log(arr.reverse());//[5, 4, 4，3, 2, 1]console.log(arr.concat(arr1));//[5, 4, 4, 3, 2, 1, "love", 99]console.log(arr.sort());//[1, 2, 3, 4, 4， 5]

3.slice(startIndex, endIndex) //Intercept the (endIndex-startIndex) data starting from startIndex, characters String arrays are acceptable. If endIndex is negative, it is equivalent to (endIndex + original data length). The original data remains unchanged after the operation.

var  arr = [1,'two',3];var arr1 = 'love';
console.log(arr.slice(1,-1));//['two']console.log(arr.slice(1,3));//["two", 3]console.log(arr1.slice(1,3));//ov

4.数学方法

    Math.random()  // 0~1随机数
    Math.pow(x，y)  // x的y次方
    Math.sqrt(x)  // x开2次方
    Math.abs()  // 绝对值
    Math.floor(x)  // 少于等于x的最大整数
    Math.ceil(x)  // 大于等于x的最小整数
    Math.round(x)  // 四舍五入
    Math.max(x, y, z)  // 返回最大值
    Math.min(x, y, z)  // 返回最小值

     var a = 3.4;     var b = 6.6;
     console.log(Math.random());//0-1随机数 console.log(Math.pow(a,3));//39.3--a的3次方 console.log(Math.sqrt(a));//1.84--开2次方 console.log(Math.abs(a));//绝对值 console.log(Math.floor(a));//3--少于等于a的最大整数 console.log(Math.ceil(a));//4--大于等于a的最小整数 console.log(Math.round(a));//3--四舍五入 console.log(Math.max(a,b,1));//6.6--返回最大值 console.log(Math.min(a,b,1));//1--返回最小值

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