Built-in objects (arrays, Boolean, number, strings) and custom objects in JavaScript

The built-in objects commonly used in JS are: Arrays, Boolean classes, number classes, strings. The following describes the respective common methods

The array in JS

1. Declaration of an array
The ① literal declaration uses the [] Declaration array directly:
var arr=[1,2, "3", true,null,undefined];

in JS, the same array can hold various data types.

② using the New keyword declaration: var arr = new Array ();
parameters can be in three different forms:
>>> does not pass parameters, which means to create an empty array of length 0;
>>> passes in a numeric value that represents the creation of an array of length. But the length of the array in JS can be changed dynamically at any time;
>>> passes in multiple values, representing the creation of an array and the values as array elements.

2. Reading and deleting elements in the array:
① uses [] to read array elements.
② The additions and deletions of elements in the array:

>>> Delete elements in an array: Delet arr[1];
>>>. Push (): Appends an element to the end of the array
>>> pop (): means to delete the last element of an array
>>> Shift (): Delete the first element of an array
>>>. Unshift (): Inserts a new element at the beginning of the array

various methods of arrays in 3.JS:
①.join ("-"): An incoming delimiter that is used to concatenate an array into a string with the specified delimiter.
If the parameter is set to NULL, the default is separated by commas.
②.concat (): Joins two or more arrays, returns a new array after the connection, and if the concatenated array is a two-dimensional array, only one layer is opened;

[1,2].concat ([3,4])-->[1,2,3,4]
[1,2].concat ([3,4,[5,6]])-->[1,2,3,4,[5,6]

③.sort (): Sorts the array.
>>> By default, the ASCII code will be sorted in ascending order;
The >>> parameter can be passed directly to the comparison function:
Arr.sort (function () {
return a-b;//Ascending
return b-a;//Descending
});

④.reverse (): Flips the element order of the original array.

⑤.slice (start,end): Receives two values, intercepts a sub-array, and returns.
>>> Pass in a value indicating that the current subscript starts at the end;
>>> Pass in two values indicating that the end is truncated from start, with start not containing end
>>> start and end can be negative. Positive numbers indicate left to right, starting from 0;
negative numbers indicate right-to-left, starting from 1.

⑥.indexof (): Finds the index of the first occurrence of an array element
. LastindexOf (): Finds the last occurrence of an array element subscript

⑦.foreach (); receives a callback function that iterates through the array
[This function is not available until IE8]
. ForEach (function (item,index) {
Console.log (item+ "-------" +index);
});

⑧.map (): array mapping, in the callback function, you can have a return value. Represents each value that will be returned, assigned to a new array.
[This function is not available until IE8]
var arr1=arr.map (function (Item,index,arr) {
return item;
});

Boolean class

The Boolean class is declared in two ways: the literal declaration and the New keyword declaration.

1. Use the new keyword to declare the variable, with typeof detection is the object type;

2. Use literal declaration of variables, with typeof detection is a Boolean type

If you do not use the New keyword directly as a Boolean () function, you can convert various data types to variables of type Boolean

Number class

The common methods of the number class are:

1. ToFixed (2): Converts the numeric value to a string, rounding it, preserving the decimal number of the specified digits.

2. ToString (): Convert numeric value to string

3. toLocaleString (): Converts values to a string in local format, thousands separators, and a group of three numbers.

(12,345,678.5678)

4. ValueOf (): Takes the object type to the base numeric value.

String

1. The. Length property returns the lengths of a string
2. Read each character in the string:
Str[0] or Str.charat (0)
3. Other common methods:

①.tolowercase (): Convert string to lowercase
②.touppercase (): Convert string to uppercase
③.substring (INDEX1,INDEX2): Returns the string between Index1 and Index2, including the index1 corresponding character, not including the index2 corresponding character
④.indexof (): Find where a character value first appears in a string
⑤.lastindexof (): Finds the last occurrence of a specified character or substring in a string
⑥.split (""): passing in the specified character, splitting the string into multiple substrings, returning an array of type string
⑦.replace (/h/g, "*"): If the first argument is a string, you can only replace the first string, and if you want to replace more than one, use a regular expression.

js the declaration of a custom object

1. Use literal declaration:
var obj={
Age:14,
Name: "Zhangsan",
Func:function () {
}
}

Attention:
① between attributes and property values: Separates the key-value pairs
② multiple pairs of attributes, separated by commas
The key of the ③ object, which can be a variety of data types (except array [] and object {}).
The value of the object, which can be a variety of data types

2. Declaring with the New keyword
var obj1=new Object;
Obj1.name= "Zhangsan";
Obj1.func=function () {
}

3. Reading and writing of object properties and methods
① use, invoke
Outside the object, you can use the Obj.age
Inside the object, you can use Obj.age or this.age

Note: In an object, using the variable name directly defaults to using a global variable. If you want to use the object's properties, you must call the object name or this
② using [key] Call: Obj[age] obj[1] obj["name"]
If the key of the object contains special characters, it cannot be used. When called, you can call with brackets.

4.obj.hasownproperty (keys) detects if a key belongs to an object

5.delete Obj.name Delete an object's properties

Built-in objects (arrays, Boolean, number, strings) and custom objects in JavaScript