Summary of array methods

Push () method

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

let arr = [1.2.3.4] 
console.log(arr.push(5)) //5 returns the length of the new array
console.log(arr) / / [1, 2, 3, 4, 5]
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Pop () method

Deletes the last element of the array and returns the last element of the array to be deleted

let arr = [1.2.3.4] 
let num = arr.pop() 
console.log(num) //4, return the deleted element
console.log(arr) / / [1, 2, 3]
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Unshift () method

Adds one or more elements to the front of the array and returns a new length header addition

let arr = [1.2.3.4] 
console.log(arr.unshift(5.1)) // return the length of the new array
console.log(arr) / /,1,1,2,3,4 [5]
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The shift () method

Deletes the array head element and returns the deleted element head deletion

let arr = [1.2.3.4] 
let num = arr.shift() 
console.log(num) //1 returns the length of the new array
console.log(arr) / / / 2 and 4
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Splice () method

Deletes and modifies an array to return an array of deleted elements

Syntax: splice (index, length, added element 1, added element 2…)

Parameter description:

  • Index: Index of the element to be deleted

  • Length: indicates the length to be deleted

  • Added element: The element added starting with index is added to the deleted array to add the new array

let arr = [1.2.3.4.5] 
// select the element with index 1 from the array and delete 3 elements ====> delete 2,3,4
// Add elements 1,[1,2],[1,2,3] from array index 1
let reArr3 = arr.splice(1.3.1[1.2], [1.2.3]) 
console.log(reArr3) //[2,3,4], returns an array of deleted elements
console.log(arr) / / [1, 1, [1, 2], [1, 2, 3], 5]
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Slice () method

Clipping the current array returns a new array containing the clipped values, unchanged from the original array

Syntax: slice (starIndex, endIndex)

Parameter description:

  • StarIndex: The starting position of the clipping, which returns an array containing the value of the starting position

  • EndIndex: position at the end of the clipping, excluding the value of the end position

let arr = [1.2.3.4.5] 
let newArr = arr.slice(2.4) 
console.log(newArr) / / [3, 4]
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Concat () method

Merges two or more arrays, returns a new array, does not alter the original array

let a = [1.2.3] 
let b = [2.3.4] 
let c = a.concat(b) 
console.log(c) / /,2,3,2,3,4 [1]
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The join () method

Converts an array to a string without changing the original array. This method returns the converted string, separated by, by default

let arr = [1.2.3.4] 
console.log(arr.join())/ / 1, 2, 3, 4
console.log(arr)/ / [1, 2, 3, 4]
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The reverse () method

Used to reverse the order of the elements in an array, returning the reversed array, changing the original array

let arr = [1.2.3.4.5] 
let re = arr.reverse() 
console.log(re) / /,4,3,2,1 [5]
console.log(arr)/ /,4,3,2,1 [5]
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IndexOf() and lastIndexOf() methods

Both return the element’s first position in the array, or -1 if not found

The difference is: indexOf looks up from the beginning. LastIndexOf looks up from the tail

Syntax: indexOf(element, startIndex) lastIndex(element, startIndex)

Parameter Description:

  • Element: The element to be found

  • StartIndex: the index to start the search

The filter () method

Returns the elements that meet the criteria to form a new array, unchanged

Grammar: filter (function (item, index, ‘arry) {})

Parameter Description:

  • The callback determines whether item meets the criteria on each iteration
let arr = [1.2.3.4.5] 
let re = arr.filter((item) = >{ 
   return item > 3 
}) 
console.log(arr) / / [1, 2, 3, 4, 5]
console.log(re) / / (4, 5)
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The map () method

Each element in the array is called once, and the callback is returned in a new value, unchanged

Map (function(item,index,arr){}

Parameter Description:

  • Is a callback function that is executed on the mig element during traversal
let arr = [1.2.3.4] 
let re = arr.map((item,index,arr) = >{ 
    return item*10 
}) 
console.log(re);// [10, 20, 30, 40]; 
console.log(arr);// [1, 2, 3, 4]
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Every () method

Determines whether an element in an array satisfies a condition. Returns true if each element satisfies a condition, false otherwise

Every (function(item,index,arr){})

let array = [1.2.3.4]; 
let bo = array.every((item, index, array) = >{return item > 2; 
}); 
console.log(bo);  // false;
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Some () method

Search for a value that satisfies the condition, and stop immediately if it is found, returning true if it is found, false if it is not.

Grammar: some (function (item, index, arr) {})

let array = [1.2.3.4.6]; 
let temp = array.some((item, index, array) = > {
    return item > 5; 
}); 
console.log(temp);// true
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The forEach () method

Iterate through the array without interrupting

Grammar: forEach (function (item, index, array) {}, this)

Parameter Description:

  • Item: The element currently traversed by the array. By default, the array elements are fetched from left to right

  • Index: The index of the current elements in the array. The first element has an index of 0, which is accumulated successively

  • Arr: array currently traversed

  • This: The reference to this in the callback function

let arr = [1.2.3.4.5]
let obj = {a:1}
arr.forEach(function(item,index,arr){
  console.log(The current element is${item}The index for${index}, belongs to an array${arr}`);
  console.log(this);/ / this point to obj
},obj)

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