Detailed explanation of common methods of JavaScript Array

Methods that do not change the original array

1. concat

Used to merge two or more arrays. This method does not mutate the existing array but returns a new array.

grammar:

var new_array = old_array.concat(value1[, value2[, ...[, valueN]]])

parameter:

ValueN (optional):

Arrays and/or values ​​that will be merged into a new array. If all valueN parameters are omitted, concat returns a shallow copy of the existing array on which this method is called.

Return value:

A new Array

2. join

Concatenates all the elements of an array (or an array-like object) into a string and returns the string. If the array has only one item, that item is returned without the separator.

grammar:

arr.join([separator])

parameter:

separator (optional):

Specifies a string to separate each element of the array. If necessary, convert the delimiter to a string. If this value is omitted, array elements are separated by commas (,). If separator is the empty string (""), then no characters are placed between all elements.

Return value:

A string with all array elements concatenated. If arr.length is 0, an empty string is returned.

Notice:

If an element is undefined or null, it is converted to an empty string.

3. Slice

Returns a new array object that is a shallow copy of the original array determined by begin and end (including begin and excluding end). The original array is not changed.

grammar:

arr.slice([begin[, end]])

parameter:

begin (optional): The index at which the extraction starts (starting from 0), from which the original array elements are extracted. If the parameter is a negative number, it means to start extracting from the last element in the original array. Slice(-2) means to extract the second-to-last element to the last element (including the last element) in the original array. If begin is omitted, the slice starts at index 0. If begin exceeds the index range of the original array, an empty array is returned.

end (optional): The index (starting from 0) at which the extraction ends, at which the extraction of the original array elements ends. slice extracts all elements in the original array with indexes from begin to end (including begin but not including end). If this parameter is a negative number, it indicates the last element in the original array at which extraction ends. If end is omitted, the slice will be extracted to the end of the original array. If end is greater than the length of the array, slice will be extracted to the end of the original array.

Return value:

A new array containing the extracted elements.

4. toString

Returns a string representing the specified array and its elements.

grammar:

arr.toString()

Return value:

A string representing the specified array and its elements.

How to change the original array

1. Pop

Removes the last element from an array and returns the value of that element.

grammar:

arr.pop()

Return Value

The element to remove from the array (returns undefined if the array is empty).

2. Push

Adds one or more elements to the end of an array and returns the new length of the array.

grammar:

arr.push(element1, ..., elementN)

parameter:

elementN : The element to be added to the end of the array.

Return value:

When this method is called, the new length property value is returned.

3. Shift

Removes the first element from an array and returns the value of that element. This method changes the length of an array.

grammar:

arr.shift()

Return value:

The element removed from the array; returns undefined if the array is empty.

4. unshift

Adds one or more elements to the beginning of an array and returns the new length of the array (this method modifies the original array).

grammar:

arr.unshift(element1, ..., elementN)

parameter:

elementN: The element or elements to be added to the beginning of the array.

Return value:

When this method is called on an object, the value of its length property is returned.

5. splice

Modifies an array by removing or replacing existing elements or adding new elements in place, and returns the modified contents as an array. This method mutates the original array.

grammar:

array.splice(start[, deleteCount[, item1[, item2[, ...]]]])

**parameter:**

start​​ : Specifies the starting position of the modification (counting from 0). If the length of the array is exceeded, content is added from the end of the array; if it is a negative value, it indicates the number of bits from the end of the array (counting from -1, which means -n is the nth element from the end and is equivalent to array.length-n); if the absolute value of the negative number is greater than the length of the array, it indicates that the starting position is 0.

deleteCount (optional): An integer representing the number of array elements to remove. If deleteCount is greater than the total number of elements after start, all elements after start will be deleted (including the start position). If deleteCount is omitted or its value is greater than or equal to array.length - start (that is, if it is greater than or equal to the number of elements after start), then all elements of the array after start are deleted. If deleteCount is 0 or negative, no elements are removed. In this case, at least one new element should be added.

item1, item2, … (optional): elements to be added to the array, starting from position start. If not specified, splice() will simply remove array elements.

Return value:

An array consisting of the elements that were removed. If only one element is removed, an array containing only one element is returned. If no elements were removed, an empty array is returned.

6. reverse

Reverses the position of the elements in an array and returns the array. The first element of the array becomes the last, and the last element of the array becomes the first. This method will mutate the original array.

grammar:

arr.reverse()

Return value:

The reversed array.

7. sort

Sorts the elements of an array using an algorithm and returns the array.

grammar:

arr.sort([compareFunction])

parameter:

compareFunction (optional): A function used to specify an order. If omitted, the elements are sorted according to the Unicode positions of the characters in the converted string.

1. firstEl : The first element to be compared.

2. secondEl : The second element to be compared.

Return value:

The sorted array.

Summarize

This article ends here. I hope it can be helpful to you. I also hope you can pay more attention to more content on 123WORDPRESS.COM!