Array common methods

Common Array object methods

• concat()
  • Joins two or more arrays
  • Do not change the original array
  • Returns a copy of the joined array

    let a = [1.2.3]
    let b = [3.4.5]
    let c = a.concat(b)
    console.log(a) / / [1, 2, 3]
    console.log(b) / / / three, four, five
    console.log(c) / /,2,3,3,4,5 [1]
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• join()
  • Delimits the data in the array using the specified delimiter and returns a string
  • Do not change the original array
  • Return string

        let a = [1.2.3]
        let b = a.join('. ')
        console.log(a) // 1，2，3
        console.log(b) / / 1.2.3
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• slice()
  • Returns the element at the selected position from an existing array summary
  • Do not change the original array
  • Returns a new array

    let a = [1.2.3]
    let b = a.slice(0.2)
    console.log(b) / / [1, 2]
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• toString()
  • Convert an array to a string
  • Do not change the original array
  • Returns the string form of an array

    let a = [1.2.3]
    let b = a.toString(a)
    console.log(b) / / 1, 2, 3
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• pop()

  • Deletes the last element of the array. If the array is empty, the array is not changed and undefined is returned

  • Change the original array

  • Returns the deleted array

    let a = [1.2.3]
    let aa = []
    let b = a.pop()
    let bb = aa.pop()
    console.log(b) / / 3
    console.log(bb) // undefined
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• push()
  • Adds one or more elements to the end of the array
  • Change the original array
  • Returns the length of the new array (no return value, no chain structure)

    let a = [1.2.3]
    let b = a.push(4.5.6)
    console.log(a) // [1, 2, 3, 4, 5, 6] changes the original array
    console.log(b) / / 6
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• reverse()
  • Reverses the order of the elements in an array
  • Change the original array
  • Return the array

    let a = [1.2.3.4]
    let b = a.reverse()   
    console.log('a',a) //a [4, 3, 2, 1] changes the original array
    console.log('b',b) //b [ 4, 3, 2, 1 ]
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• shift()
  • Delete the first element of the array, if the array is empty, do not operate, return undefined
  • Change the original array
  • Returns the value of the first element removed

    let a = [1.2.3.4]
    let b = a.shift()
    console.log(a)// [2, 3, 4] √
    console.log(b)/ / 1
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• sort()
  • Sort array elements (according to the ASCII table)
  • Change the original array
  • Return the array

    let a = [3.2.1]
    let b = a.sort()
    console.log(a) // [1, 2, 3] changes the original array
    console.log(b) // [1, 2, 3]
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• splice()
  • Adds/removes items from an array
  • Change the original array
  • Returns the deleted element

    let a = [1.2.3.4]
    let b = a.splice(1)
    console.log(a) // [1] Changes the original array
    console.log(b) // [2, 3, 4] returns the deleted element
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• unshift()
  • Adds one or more elements to the beginning of an array
  • Change the original array
  • Returns the length of the new array

    let a = [1.2.3.4]
    let b = a.unshift(-1.0)
    console.log(a)  // [-1, 0, 1, 2, 3, 4]
    console.log(b) // The length returned by 6
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