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preface

  • You learned about the new ES6 functions in the previous article
  • This article introduces two new data structures called Set Map

Set

  • A Set is a data structure for a collection

    • A collection of disordered, related, and non-repeating elements
    • Like an array, all elements have unique values
    • The Set itself is the constructor used to generate the Set data structure
    let a = new Set(a)Copy the code
    • Set add delete change check method
    • addAdding a value returns the Set itself
    let a = new Set()
a.add(1).add(1) // 1 is added only once. Set does not allow duplicate elements
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    • deleteDeleting an element returns a Boolean value
    let a = new Set()
a.add(1).add(2) / / {1, 2}
a.delete(1) // true
a / / {2}
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    • hasReturns a Boolean value that checks whether the element exists in the set
    let a = new Set()
a.add(1) / / {1}
a.has(1) // true
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    • clearClears all elements with no return value
    let a = new Set()
a.add(1).add(3) / / {1, 3}
a.clear()
a / / {}
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  • Set traversal method

    • keysReturns a traverser for the key name
    let a = new Set([1.2.3])
for(let item of a.keys) {
    console.log(item) / / 1 2 3
}
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    • valuesReturns a traverser for key values
    let a = new Set([1.2.3])
for(let item of a.values) {
    console.log(item) / / 1 2 3
}
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    • entriesReturns a traverser for key-value pairs
    let a = new Set([1.2.3])
for(let item of a.values) {
    console.log(item) / / [1, 1] [2] [3, 3]
}
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    • forEachUse the callback function to iterate over each element
    let a = new Set([1.2.3])
a.forEach((value,key) = >{console.log(`${key}:${value}`)})
/ / 1:1 2:2 3-3
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    • The extension operator and set are used to implement array de-duplication
    let arr =  [1.2.3.3.2.1]
let arr2 = [...new Set(arr)] / / [1, 2, 3]
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Map

  • An ordered list of key-value pairs keys and values can be of any type

    • The map itself is the constructor used to generate the map structure
    let map = new Map(a)Copy the code

  • Add, delete, modify, and check map

    • Size Returns the number of elements in the map structure
    let map = new Map()
map.set(1.2)
map.size / / 1
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    • Set sets the key name and key value and returns map overridden if the key name is the same
    let map = new Map()
map.set(1.2).set(3.4) // use the chaining method
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    • Get Reads the value of the key and returns undefined if the key is not found
    let map = new Map()
map.set(1.2).set(3.4) / / {1 = > 2, 3 = > 4}
map.get(1) / / 2
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    • Has finds whether a key returns a Boolean value in the current map
    let map = new Map()
map.set(1.2) / / 1 = > {2}
map.has(1) //true
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    • Delete Deletes a key and returns a Boolean value
    let map = new Map()
map.set(1.2).set(3.4) / / {1 = > 2, 3 = > 4}
map.delete(1) //true
map / / 3 = > {4}
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    • Clear Clears all elements with no return value
    let map = new Map()
map.set(1.2).set(3.4) / / {1 = > 2, 3 = > 4}
map.clear
map / / {}
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  • The Map of traverse

    • Keys returns a traverser for the key name
    let map = new Map([['a'.1],
    ['b'.2]])for(let item of map.keys()) {
    console.log(item)  // 'a' 'b'
}
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    • Values returns a traverser for key values
    let map = new Map([['a'.1],
    ['b'.2]])for(let item of map.values()) {
    console.log(item)  / / 1. 2
}
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    • Entries return a traverser for key – value pairs
    let map = new Map([['a'.1],
    ['b'.2]])for(let item of map.entries()) {
    console.log(item)  // ['a',1] ['b',1]
}
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    • ForEach traverses all elements of the map
    let map = new Map([['a'.1],
    ['b'.2]
])
map.forEach((value,key) = >{
    console.log(key,value)
})
// a 1 b 2
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The difference between Set and Map

  • In common
    • Collections and dictionaries can store values that are not duplicated
  • The difference between
    • Collections store elements as [values, values] and dictionaries as [keys, values]

conclusion

  • Today’s lesson
  • “Feel free to discuss in the comments section, nuggets officials will be onProject DiggAfter the event, 100 nuggets will be selected in the comments section. Details can be found in the event article.