Three built-in objects for js basic improvement learning

This time I will bring you three built-in objects to improve the basics of js. What are the precautions for using the three built-in objects of js? The following is a practical case, let's take a look.

Here we only understand the three major built-in objects, namely string, time, and array

What are built-in objects?

Built-in objects refer to some objects that come with the language for developers to use. These objects provide some commonly used or the most basic and necessary functions. The built-in objects of JS running on the browser include Math, String, Array, Date, and the location mentioned above. You can use these objects, but modification is generally not recommended. (Lenovo python for learning)

As a programming language, JavaScript provides some built-in objects and functions. Built-in objects provide several of the most commonly used functions in programming. There are the following types of JavaScript built-in objects.

● Object:

● String object: handles all string operations

● Math object: handles all mathematical operations and helps us complete complex operations (static method )

● Date object: handles the storage, conversion and expression of date and time

● Array object: provides an array model and stores a large amount of ordered data

● Event object: Provides various processing information for JavaScript events

Object(), Date(), String(), Array(), Math (of course Number, Boolean, Regular ExpressionRegExp, Function, I won’t go into details about these). The following is a brief introduction to the properties and methods frequently used by these five objects.

Built-in objects have their own methods and properties. The access methods are as follows:

Object name.Attribute name

Object name.Method name (parameter list)

1. String object:

Generally use the functions provided by the String object to process strings. String mainly provides the following methods for processing strings.

● charAt(idx): Returns the character at the specified position

● indexOf(Chr): Returns the position of the specified substring, from left to right. Not found returns -1.

● lastIndexOf(chr): Returns the position of the specified substring, from right to left. Not found returns -1.

● toLowerCase(): Convert all characters in the string to lowercase.

● toUpperCase(): Convert all characters in the string to uppercase.

str.length Search string in string: indexOf(); Content matching: match(); Replacement content: replace("Native target parameter", "Replaced parameter") or replace(RegExp ,replacement); Case conversion:

toUpperCase()/toLowerCase() Split into array: str.split(“,”)

Also, charAt(), charCodeAt() , concat(), valueOf(), substr(), slice(), lastIndexOf(), substring(), search()...

The following is the detailed function of string:

Function 1: Calculate the length of the string

The space in the middle does not count

2. Math object

Math object

Method:

Math.pow(n,m) n m power.

Math.abs(n) The distance from n to the origin (the absolute value of n).

Math.round(n) Rounding to an integer.

Math.floor(n) Floor function (rounded down).

Math.ceil(n) Ceiling function (rounded up).

Math.random() Returns a random number from 0-1 (cannot get 1).

Note: [n, m] random numbers are used to obtain n, m Math.floor(Math.random())*(m-n 1) n).

Special characters

\r Carriage return

\n Line feed

Note that in python random is derived from mathematical objects It is separated from , and is still included in mathematical objects in other languages

The Math object is not an object class like Date and String, so there is no constructor Math(), so things like Math.sin() are just Functions are not methods of objects. By using Math as an object, you can call all its properties and methods, such as:

round()

Math.round(2.5)=3; random(); parseInt(Math.random() *10); max(); min(); abs() absolute value;

# #3. Time object:

The time object is a built-in object of JavaScript and must be declared before use.

Basic syntax

var curr=new Data();

Note the usage of the keyword new here, the first letter of Data() must be capitalized.

Syntax explanation

Use new to declare a new object entity. The syntax for using the new operator is as follows:

Instance object name = new object name (parameter list)

The Date object provides the following three types of methods:

● From the system Get the current time and date

● Set the current date and time

● Complete the conversion between time, date and string

The following table introduces the most commonly used Methods to obtain system time and date

Methods for processing time and date in Date object

Processing dates and events

var date =new Date(); Common methods:

getFullYear(); getTime() milliseconds; setFullYear(), eg, date.setFullYear(2010,1,1); getDay(), get the day of the week; getDate(), get the day; getHours() get the hours; getMinutes(); getSeconds();

getMonth() 0~11.

I believe you have mastered the method after reading the case in this article. For more exciting information, please pay attention to other related articles on the php Chinese website!

Recommended reading:

Basic data types for js basic improvement learning

##How to use JS to customize hash tables and sequential lists

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