Javascript Basics series: Common methods for parsing arrays

1. Implement the method of adding, deleting and changing the array

This part of the method will modify the original array

push

Push: Add content to the end of the array @params multiple arbitrary types @return The length of the array after the addition

let ary = [10.20]
let res = ary.push(12.30)
console.log(res) / / 4
console.log(ary) // [10, 20, 12, 30
// Methods that operate on key-value pairs based on native JS can also append a new item to the end
ary[ary.length] = 40
console.log(ary)
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unshift

Unshift: Adds content to the beginning of the array @params Multiple arbitrary types @return The length of the array after the addition

let ary = [10.20]
let res = ary.unshift(12.30)
console.log(res) / / 4
console.log(ary) // [10, 20, 12, 30]
// Clone the original ARY based on the native ES6 expansion operator, create the first item in the new array, the rest of the content using the original ARY information, also calculate
// Append to start
ary = [100. ary]console.log(ary)
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shift

Shift: Deletes the first item in the array @params@return deletes the item

let ary = [10.20.12.30]
let res = ary.shift()
console.log(res, ary) // 10 [20, 12, 30]
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Based on the delete in native JS, the array is treated as an ordinary object, which can indeed delete a certain content, but will not affect the structural characteristics of the array itself (the length length will not be changed). In real projects, such deletion can be eliminated by using POP

Pop: Removes the last item in the array @params

@return The item deleted

let ary = [10.20.30.40]
let res = ary.pop();
console.log(res, ary) // 40, [10, 20, 30]


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Based on native JS, the array length is removed by one bit, and the last item is removed by default

let ary = [10.20.30.40]
ary.length--;
console.log(ary)
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splice

Splice: Achieve an array of add, delete, modify @ params n, m are all digital, removed from the index n m elements (m don’t write, delete to the end) n, m, x, removed from the index n m elements, use x occupied delete part n, 0, x from the beginning of the index n, a don’t delete, Put x in front of index n. @return stores the deleted portion in a new array

let ary = [10.20.30.40]
let res = ary.splice(2.2)
console.log(res, ary)
// This method is used to empty an array and store the contents of the original array in the new array
//ary.splice(0)


// Delete the last and first items
ary.splice(ary.length-1)
ary.splice(0.1)
console.log(ary)

Append to the end of the array
ary.splice(ary.length,0.'aaa')

// Start appending to the array
ary.splice(0.0.'aaa')
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3. Convert arrays to strings

The original array stays the same

toString

ToString: Converts an array to a string @params@return converted string, separated by commas (original array unchanged)

let ary = [10.20.30]
let res = ary.toString();
console.log(res) 10, 20, 30 "/ /"
console.log([].toString()) / / ""
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join

Join: Convert an array to a string @params specified delimiter (string format) @return converted string, each entry separated by the specified delimiter (original array unchanged)

let ary = [10.20.30]
let res = ary.join(' ');
console.log(res) 10 20 to 30 "/ /"

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5. Sort or arrange arrays

reverse

Reverse: Reverses the array. @return changes the original array

let ary = [12.15.9.28]
ary.reverse();
console.log(ary)
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sort

Sort: @params can have no, or it can be a function @return after sorting the new array, the original array changes

If you do not pass an argument, you will not be able to sort numbers above 10 (it defaults to the first character).

// To sort properly, we need to pass sort a function that returns a-b ascending and b-a descending
let ary = [10.12.15.22.28.9]
ary.sort((a, b) = > {
  // A and b are adjacent terms
	 return a-b
})
console.log(ary)
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Deduplicating an array

2. 2

1. So let’s take each of the items in the array separately
2. Compare this item with each item that follows it. If it encounters an item that is identical to the current item, the item is removed from the array using the splice method

var ary = [1.2.3.1.2.1.2.1.2.3.2.1.2.3];
for(var i = 0 ; i < ary.length; i++) {
  
  // item: the current item taken out of each loop
	var item = ary[i];
  // Compare the current item with each subsequent item (loop)
  for(var j= i+1; j< ary.length; j++) {
  	var compare = ary[j];
    
    // If compare and item are equal, this item is repeated, we delete it
    if(compare === item) {
    	// the j index should be removed from the array
      ary.splice(j, 1);
      
      // The array is collapsed: each index after j is advanced by one bit. The next index to be compared should be jj--; }}}Copy the code

4. Set deduplication method based on ES6

let ary = [12.23.12.15.25.23.25.14.16]
ary = [... new Set(ary)];
console.log(ary)
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