Related examples of Math, arrays, and Date

math, arrays and dates are often encountered in learning, and this article will explain them.

Write a function that returns a random integer between min and max, including min but not including max

function getRandom (min,max) {    return Math.floor(Math.random()*(max-min) + min)
}//Math.floor 返回小于参数值的最大整数//Math.random 返回[0,1)之间的随机数

Write a function that returns a random integer between min and max, including min Including max

function getRandom (min,max) {    return Math.floor(Math.random()*(max-min+1) + min)
}

Write a function to generate a random string of length n. The value range of the string characters includes 0 to 9, a to z, A to Z

function getRandomStr (n) {    var dict = '0123456789'+               'abcdefghijklnmopqrstuvwxyz'+               'ABCDEFGHIJKLMNOPQRSTUVWXYZ'; //一个字典；
    var string = &#39;&#39;;    for (i=0; i<n; i++) {
        string += dict[Math.floor(Math.random()*62)] ;
    }    return string ;
}

Write A function that generates a random IP address. A legal IP address is 0.0.0.0~255.255.255.255

function getRandIP(){    var ipArr = [];    for (i=0; i<4; i++) {
        ipArr.push(Math.floor(Math.random()*256)); //push()方法把元素从尾部放进数组；
    }    return ipArr.join(&#39;.&#39;);
}var ip = getRandIP()console.log(ip)

Write a function that generates a random color string. The legal color is #000000~ #ffffff

function getColor () {    var dict = '0123456789abcdef'
    var color = &#39;#&#39;;    for (i=0; i<6; i++) {
        color += dict[Math.floor(Math.random()*16)];
    }    return color;
}
getColor() ;

What are the functions of push, pop, shift, unshift, join, and splice in array methods? Use the splice function to implement the push, pop, shift, and unshift methods respectively.

The push() method can insert an element from the tail into the array and change the length and index of the original array;

var a =[] ;
a.push(4);
a ; // [4]

pop() method can delete and return the last element of the array and change the length and index of the original array ;

var a =[1,2] ;
a.pop(); // 2a ; // [1]

shift() method can convert the array Delete the first element from it and return the value of the first element, changing the length and index of the original array;

var a=[1,2,3,4];
a.shift (); //1;a; //[2,3,4]

The unshift() method adds one or more elements to the beginning of the array and returns the new length, changing Original array length and index;

var a=[1,2,3,4,5];
a.unshift(7,8); //7a; //[7,8, 1,2,3,4,5]

The splice() method can add/remove items to/from the array, and then return the deleted item. If it is not deleted, it will return an empty array and change the original Array length and index;

var a=[1,2,3];
a.splice(0,1); //[1]; //Start from position 0, delete 1 bit; a; //[2,3]
var a=[1,2,3];
a.splice(0,0,7,8); //[]; from bit 0 Start, delete 0 bits, insert 7,8 (inserted before); a; //[7,8,1,2,3];
var a=[1,2,3,4];
a.splice(1,1,7,8); //[2]; Starting from position 1, delete 1 position ([2]) and insert 7,8; ​​a; //[1,7,8 ,3,4];

Use splice() to implement push(), pop(), shift(), and unshift() methods;

var a =[1 ,2,3,4,5,6];
a.splice(a.length,0,n) // Implement push(), n is the element you want to pass in; a.splice(a.length -1,1) // Implement pop(); a.splice(0,1) // Implement shift(); a.splice(0,0,n) // Implement unshift(), n is what you want to pass in elements;

Write a function, operate the array, each item in the array becomes the original square, operate on the original array

function squareArr(arr){    for (i=0; i<arr.length; i++) {
        arr[i] = arr[i]*arr[i];
    }    return arr;
}var arr = [2, 4, 6]
squareArr(arr)console.log(arr) // [4,16,36]

Write a function, operate the array, return A new array, the new array only contains positive numbers, the original array remains unchanged

function filterPositive(arr){    var newArr = [];    var k = 0;    for (i=0; i<arr.length; i++) {        if (typeof arr[i] === &#39;number&#39;) {  //验证是否为数字
            if(arr[i]>0) {
                newArr[k] = arr[i];
                k++;
            }
        }
    }    return newArr;
}var arr = [3, -1,  2,  &#39;饥人谷&#39;, true]var newArr = filterPositive(arr)console.log(newArr) //[3, 2]console.log(arr) //[3, -1,  2,  &#39;饥人谷&#39;, true]

Write a function getChIntv to get the interval from the current time to the specified date

//示例var str = getChIntv("2017-02-08");console.log(str);  // 距除夕还有 20 天 15 小时 20 分 10 秒
 function getChIntv(date) {    var time = Math.abs(Date.now()-Date.parse(date));    var day = Math.floor(time/86400000);    var hour = Math.floor(time%86400000/3600000);    var min = Math.floor(time%86400000%3600000/60000)    var s = Math.floor(time%86400000%3600000%60000/1000)    var ms = (time%86400000%3600000%60000%1000);    return '距离'+date+': '+day+' 天 '+hour+' 小时 '+min+' 分钟 '+s+' 秒 '+ms+' 毫秒 '}
getChIntv('2017-04-08')  //距离2017-04-08: 55 天 4 小时 0 分钟 45 秒 774 毫秒；

Put hh-mm- Change the dd format digital date to Chinese date

//示例var str = getChsDate('2015-01-08');console.log(str);  // 二零一五年一月八日
var dict ={0:'零',1:'一',2:'二',3:'三',4:'四',5:'五',6:'六',7:'七',8:'八',9:'九',            10:'十',11:'十一',12:'十二',13:'十三',14:'十四',15:'十五',16:'十六',            17:'十七',18:'十八',19:'十九',20:'二十',21:'二十一',22:'二十二',23:'二十三',            24:'二十四',25:'二十五',26:'二十六',27:'二十七',28:'二十八',29:'二十九',30:'三十',31:'三十一'} function getCHT (date) {
    time = date.split('-');
    year = time[0].split(&#39;&#39;);    for (i=0; i<year.length; i++) {
        year[i] = dict[year[i]];
    }
    month = dict[parseInt(time[1])];
    day = dict[parseInt(time[2])];    return year.join(&#39;&#39;)+&#39; 年 &#39;+month+&#39; 月 &#39;+day+&#39; 日&#39;}
getCHT(&#39;2017-06-01&#39;) // 二零一七年六月一日；

Write a function, the parameter is the string format of the time object milliseconds, and the return value is a string. Assume that the parameter is the time object millisecond t, and the following strings are returned according to the time of t:

Just now (t is less than 1 minute interval from the current time)

3 minutes ago (t is less than 1 minute interval from the current time) The current time is greater than or equal to 1 minute and less than 1 hour)

8 hours ago (t is greater than or equal to 1 hour and less than 24 hours from the current time)

3 days ago (t is greater than or equal to the current time 24 hours, less than 30 days)

2 months ago (t is greater than or equal to 30 days from the current time and less than 12 months)

8 years ago (t is greater than or equal to 12 months from the current time )

//示例function friendlyDate(time){
}var str = friendlyDate( '1484286699422' ) //  1分钟前var str2 = friendlyDate('1483941245793') //4天前
function friendlyDate(time){    var nowT = Date.now();  //Date.now()获取当前时间距离1970年1月1日00:00:00的毫秒数
    pastT = nowT-time;    if (pastT<=60*1000) {        return &#39;刚刚&#39;
    }if (pastT>60000 && pastT<3600*1000) {        return Math.floor(pastT/60000)+&#39;分钟前&#39;
    }if (pastT>=3600*1000 && pastT<24*3600*1000) {        return Math.floor(pastT/(3600*1000))+&#39;小时前&#39;
    }if (pastT>=24*3600*1000 && pastT<30*24*3600*1000) {        return Math.floor(pastT/(24*3600*1000))+&#39;天前&#39;
    }if (pastT>=30*24*3600*1000 && pastT<12*30*24*3600*1000) {        return Math.floor(pastT/(30*24*3600*1000))+&#39;月前&#39;
    }else {        return Math.floor(pastT/(360*24*3600*1000))+&#39;年前&#39;
    }
}
friendlyDate(1496246400000) //一天前；

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