Common methods of array

Array.push()

Add one or more elements... To the end of the array , And returns the new array length . The original array changes .

Array.forEach(function)

Used to call each element of an array , And pass the element to the callback function . The original array remains the same .（ Pay attention to this method and map The difference between , If you print directly Array.forEach, The result is undefined）.

Array.map(function)

After each item of the original array executes the function , Returns a new array . The original array remains the same .（ Pay attention to this method and forEach The difference between ）.

indexOf()

Detect the position index of the current value for the first time in the array

Parameters ：array.indexOf(item,start) item: Looking for elements start: The position in the string where the retrieval starts .
Return value ： The index found for the first time , No return found -1.
Whether to change the original array ： Don't change .

includes()

Determine whether an array contains a specified value .

Parameters ： Specified content
Return value ： Boolean value
Whether to change the original array ： Don't change .

Array.join()

Connect each item of the array with a specified character to form a string . The default connection character is “,” comma .

Array.filter(function)

Filter the array , Qualified elements and return a new array .

Array.some(function)

Judge each item in the array , If none of them meet the requirements, return to false, Otherwise return to true.

Array.pop()

Delete and return the last element of the array , If the array is empty , Then return to undefined. The original array changes .

Array.unshift()

Add one or more elements... To the beginning of the array , And returns the new array length . The original array changes .

Array.shift()

Delete the first item of the array , And returns the value of the first element . If the array is empty , Then return to undefined. The original array changes .

Array.concat(arr1,arr2…)

Merge two or more arrays , Generate a new array . The original array remains the same .

Array.reverse()

Reverse array . The original array changes .

Array.sort()

Sort array elements . According to the string UniCode Sort code , The original array changes .

1. From small to large
   
2. From big to small
   
3. Sort by a value in the array object
   
   

Array.slice()

Find out some of the contents according to the conditions

Parameters ：
array.slice(n, m), From the index n Start finding m It's about （ It doesn't contain m）
array.slice(n) The second parameter is omitted , Then search until the end
array.slice(0) Output content as is , Array cloning can be realized
array.slice(-n,-m) slice Support negative parameters , From the last item ,-1 For the last ,-2 It's the penultimate item
Return value ： Returns a new array
Whether to change the original array ： Don't change

Array.splice(index,howmany,arr1,arr2…)

Used to add or delete elements in an array . from index Location start delete howmany Elements , And will arr1、arr2… Data from index Insert... In sequence .howmany by 0 when , The element is not deleted . The original array changes .

Array.every(function)

Judge each item in the array , If all match, return true, Otherwise return to false.

Array.reduce(function)

reduce() Method to receive a function as an accumulator , Every value in the array （ From left to right ） Start to shrink , The final calculation is a value .