JS objects and Arrays

1. Create an array

The simplest way to create an array is to add an object directly in JavaScript code. The direct object quantity is a list of attribute names and values separated by commas (,). Each attribute name can be a javascript identifier or a string, each property value can be a constant or any JavaScript expression.

The new operator can create a specific class of objects. After new, a constructor is called to initialize the attributes of an object.

2. Objects used as correlated Arrays

We can use the operator "." to access an object attribute, while the more common access attribute operator of arrays is []. In this way, the values of the following two expressions are equal:

Object. Property

Object ["property"]

The most important difference between these two syntaxes is that the property name of the former is the identifier, and the property name of the latter is a string.

3. Common Object Attributes and Methods

All objects in JavaScript are inherited from the object class.

3.1 constructor attributes

In JavaScript, each object has a constructor attribute, which references the constructor that initializes this object.

3.2. tostring () method

This method has no parameters. It returns a string that represents the value of an object to some extent, and it is called on this object. This method is called when JavaScript needs to convert an object into a string.

3.3. tolocalestring () method

This method is used to return a localized string representation of an object. By default, this method does not localize itself. It always returns exactly the same content as tostring.

3.4 valueof () method

When JavaScript needs to convert an object to a certain basic data type, that is, a number rather than a string, it calls a method. If an object is used in an environment that requires a basic value, javascript will automatically call this method.

3.5 hasownproperty () method

If the object uses the name specified by a separate string parameter to locally define a non-inherited attribute, this method returns true. Otherwise, false is returned.

3.6. propertyisenumerable () method

If the object uses the name specified by a separate string parameter to define a non-inherited attribute, and this attribute can be enumerated in a for/in loop, propertyisenumerable () returns true. Otherwise, false is returned.

3.7 isprototypeof () method

If the object to which the method belongs is the prototype object of the parameter, the method returns true. Otherwise, false is returned.

4. Array

The simplest way to create an array is to use the array directly, which is only a list of array elements separated by commas in square brackets. The values in the direct quantity of an array are not necessarily constants. They can be any expressions. The direct quantity of arrays can contain the direct quantity of objects or other arrays.

Another way to create an array is to use the Array () constructor: No parameter call; you can explicitly specify the values of the First n elements of the array; you can pass it a numeric parameter, this number specifies the length of the array.

4.1 Delete array elements

Delete operator. An array element is set to the undefined value, but the element still exists. To delete an element so that all the elements whose subscript position is higher than it are migrated down to a lower subscript position, an array method must be used. Array. the shift () method deletes the first element of the array, array. the pop () method deletes the last element, array. splice () Removes elements in a continuous range from an array.

5. Array Method

5.1 join () method

This method can convert all elements of an array into strings and then connect them. You can specify an optional string to separate the elements in the result string. If no separator string is specified, use commas to separate elements.

5.2. Reverse () method

This method will reverse the order of array elements and return the inverted array. It performs this operation on the meta array. That is to say, it does not create a new array for elements rearranging, but rearranges the array elements in an existing array.

5.3. Sort () method

This method sorts array elements in the original array and returns the sorted array. If the parameter is not set during the call, the array elements are sorted alphabetically.

5.4 Concat () method

This method can create and return an array, which contains the elements of the original array that calls Concat (), followed by the Concat () parameter. If some of the parameters are arrays, they are expanded and their elements are added to the returned array. Note: This function does not recursively expand an array whose elements are arrays.

5.5 slice () method

This method returns a segment of the specified array, or a sub-array. Its Two Parameters specify the start and end points of the fragments to be returned. The returned array contains the elements specified by the first parameter and the elements starting from the element to the element specified by the second parameter, but does not contain the elements specified by the second parameter.

5.6. splice () method

This method is a common method for inserting or deleting array elements. It modifies the array on the original array and does not create a new array.

5.7. Push () and POP () Methods

These two methods allow us to use arrays just like using stacks.

5.8. unshift () and shift () Methods

The actions of these two methods are very similar to those of push () and POP (), except that they insert and delete elements in the header of the array, rather than at the end.

5.9. tostring () and tolocalestring () Methods

The tostring () method can convert each element of an array into a string.

Tolocalestring () is the version of tostring () method localization. It will call the tolocalestring () method of each element to convert the array element into a string, and then connect the generated string with a local specific separator string.