Math object
Math.random() generate 0---1 Random decimals between, 0 can be generated, 1 cannot be generated Math.round() Get the rounding of a number Math.ceil() ceiling function,Get the rounded up value of a number Math.floor() floor function,Get the rounded down value of a number Math.abs() Get the absolute value of a number Math.PI value of pi Math.pow(2,3) Get the power of a number console.log(Math.PI) console.log(Math.round(1.6)) console.log(Math.ceil(0.9)) console.log(Math.floor(3.9)) console.log(Math.pow(2, 10))
Date date object
var date = new Date()
Date()is a constructor and requires the keyword new,it's here, date for an instance.
var date = Date.parse(2009, 10, 25)
console.log(date) //This way of writing will count forward one month, because this is calculated by index,
//Default is one month ahead
var date1 = Date.parse('2009,10,25')
console.log(date1) //This way of writing will not, because it is in the form of a string.
var date = new Date() get date console.log(date); //toString() is called internally date.toDateString(); // foreigners like to use date.toLocalDateString(); The acquisition time is displayed differently in different browsers date.toTimeString() date.toLocalTimeString()
date conversion
var date = new Date(2005,10,1);
can accept parameters
2005，10，1 each part of the date
"2005-10-1" string date format
Represents the date in millisecond form 1128096000000
var date = Date.parse("2005-10-1");
Converts each part of a string or 2005, 10, 1 date to the millisecond form of the date, if the format of the string is not the correct format for the time NaN
Get the millisecond form of a date object
//Returns a number, time in milliseconds var date = Date.now(); //HTML5，IE9+ var date = +new Date(); //When the now method is not supported var date = new Date(); date.valueOf(); // output date in millisecond form
Get the specified part of the date
| method name | effect |
|---|---|
| getTime() | Returns the number of milliseconds as the result of valueOf() |
| getMilliseconds() | get milliseconds |
| getSeconds() | Returns the number of seconds from 0-59 |
| getMinutes() | Returns minutes from 0-59 |
| getHours() | Returns the hours from 0-23 |
| getDay() | Return day of the week 0 Sunday 6 Saturday |
| getDate() | Returns the day of the current month, the day of the month |
| getMonth() | Returns the month, starting from 0 to 9 |
| getFullYear() | Returns a 4-digit year, such as 2018 |
Array object
Introduce how to use the methods of the Array object
convert array
| method name | Paraphrase |
|---|---|
| toString() | Convert the array to a string, split each item with |
| valueOf() | Returns the array object itself |
var arr = [10,20,30,40,50,60];
// console.log(arr.toString()); // output is: 10,20,30,40,50,60,
// console.log([10, 20, 30, 40, 50, 60,70].toString());
// console.log([10,20].valueOf()); // output the original array
Manipulate arrays
| method name | Paraphrase |
|---|---|
| join() | Concatenate the elements in the array into a string, the default is to concatenate. Changes can be made within parentheses. |
| concat() | concatenate two arrays |
| slice() | Intercept a new array from the current array, without affecting the original array, the parameter start starts from 0, and the end starts from 1 |
| splice() | Delete or replace some items of the current array, parameters start, deleteCount, options (items to be replaced) |
| start: start position (subscript) deleteCount: number of deleted elements options: elements to be replaced |
var arr = [10,20,30,40,50,60];/
// var str = arr.join(); // If there are no parameters in the join method, the default is , for connection output
// var str = arr.join('%'); // If there are parameters in the join method, the current parameter is used as the connector
// var str = arr.join(''); // If you don't want to join with any characters, add a vacuum string
// console.log(str);
var strs =['aaa','bbb','ccc'];
var arr1 = arr.concat(strs);
console.log(arr1);
// slice means interception
var nums = [10,20,30,40,50,60,70];
// var nums1 = nums.slice(1,4); // start: the index to start intercepting end: the index to intercept end can not be obtained
// var nums1 = nums.slice(1); // If there is only one parameter, it means the index value to start intercepting,
//Without the second parameter, it means that it has been intercepted to the end
// console.log(nums1);
// splice intercept, replace
// nums.splice(4); // There is only one parameter, which means to intercept the first 4
// nums.splice(1,4) // When there are two parameters, the first one indicates the index to start deleting data, and the second parameter indicates the number of deletions
// nums.splice(2,3,100,200,300);// Three or more parameters represent replacement
nums.splice(2,3,"aaa","bbb","ccc");// replace
console.log(nums);
Append and delete the preceding item and the following item
| method name | Paraphrase |
|---|---|
| push() | add to the end of the array |
| pop() | delete the last one in the array |
| shift() | delete the first one in the array |
| unshift() | add to the front of the array |
var nums = [10,20,30,40,50,60];
// nums[6] = 70;
// nums[nums.length] = 70;
// var res = nums.push(70,80,90,100);
// var res = nums.push(70); // ctrl + d copy the current line to the next line
// The return value is the new length of the array after adding the array
// console.log(nums);
// console.log(res);
// var res =nums.pop(); // The pop method is used to delete the last item of data in the array
// console.log(nums);
// console.log(res); // The return value is the deleted data
// var res = nums.unshift(100,200); // unshift is used to add data to the front of the array
// console.log(nums);
// console.log(res); // return value is new length of array
var res = nums.shift(); // shift is to delete an item at the front of the array
console.log(nums);
console.log(res); // The return value is the item that was deleted
location method
indexOf() finds the position of a certain data in the data
lastIndexOf() finds the position of a certain data in the array starting from the back of the string
| method name | Paraphrase |
|---|---|
| indexOf(value[,position]) | Find the position of a character in a string |
| lastIndexOf(value[,position]) | Find the position of a character in a string starting from the back of the array |
| includes(searchValue[,start]) | Query whether an array exists from an array, and the second one indicates the starting position |
array arrangement
| method name | Paraphrase |
|---|---|
| reverse() | Invert the array, instead of returning a copy, directly manipulate the array itself |
| sort() | Even the array sort is sorted according to characters, from small to large |
check array
instanceof checks whether an array is a subclass or instance of Array
<script>
// instanceof is used to check whether it is an instance or a subclass of an array
var arr = new Array()
var nums = []
// instanceof to check whether an array is an instance object of Array
console.log(arr instanceof Array)
console.log(nums instanceof Array)
function fn(){
console.log(arguments instanceof Array) // false
// arguments.filter(function(item,index){
// console.log(item,index)
// })
}
fn(10,20,30)
</script>
iterate over an array
| method name | Paraphrase |
|---|---|
| filter(function(item,index,arr){}) | filter |
| forEach(callback) | iterate over the array |
Other similar methods are: every() some() map() reduce()
empty array
- arr.splice(0,arr.length); // delete all items in the array
- arr.length = 0; // length property can be assigned, length is read-only in other languages
- arr = []; // this method is recommended
arr.splice(0,arr.length); arr.length = 0; // length arr = [];
String
The string type is an object wrapper type for string values, which can provide us with many useful methods for manipulating strings.
var strObj = new String("hello world");
The object has methods and properties. The property length returns the total number of characters in the current string. Method Character method, string manipulation method, position method, blank removal, case conversion method...
String method
All methods of the string will not modify the string itself (the string is immutable), and a new string will be returned after the operation is completed.
character method.
charAt() //Get the character at the specified position charCodeAt() //Get the ASCII code of the character at the specified position str[0] //HTML5, IE8+ support Equivalent to charAt() concat() //Concatenate strings, equivalent to +, + is more commonly used slice() //Starting from the start position, intercepting to the end position, the end cannot be obtained substring() //Start from the start position, intercept to the end position, and the end cannot be obtained substr() //Start from the start position, intercept length characters, and intercept only one parameter to the end replace() //replace an element of a string split() // split string into array
location method
indexOf() //Returns the position of the specified content in the metastring lastIndexOf() //Search from back to front, only find the first match
remove whitespace
trim() //Only whitespace before and after a string can be removed
Case conversion method
to(Locale)UpperCase() //Convert uppercase to(Locale)LowerCase() //Convert lowercase