What is the usage of three dots in es6

Usage: 1. Merge arrays, the syntax is "[...arr1, ...arr2]"; 2. Copy array objects, the syntax is "name= [...array object]"; 3. , string to character array, the syntax is "[...string object]"; 4. Deconstructing variables, the syntax is "[variable object,...name]=value".

The operating environment of this tutorial: Windows 10 system, ECMAScript version 6.0, Dell G3 computer.

What is the usage of three dots in es6

The spread operator (spread) is three dots (...), which is a new operator in ES6. It has many functions, such as You can convert an array into a comma-separated parameter sequence, etc. In application scenarios, two types are usually used: object spread operator and array operator.

The functions are as follows:

1. Get the maximum value of the array.

Conventional: Math.max(1,2,3)

Writing: Math.max(…[1,2,3]) is equivalent to the above example

2. Call the method

function sum(a,b){
  console.log(a+b)//5
}
sum(...[2,3])

The output result is:

3. Connect the array

var arr1 = [0, 1, 2]; 
var arr2 = [3, 4, 5];  
arr1.push(...arr2);

The result array elements are 0, 1, 2, 3, 4, 5.

4. Connect the array

var arr1 = ['a', 'b']; 
var arr2 = ['c']; 
var arr3 = ['d', 'e'];
[...arr1, ...arr2, ...arr3]

The connected array elements For: a, b, c, d, e

5. Convert the string to a real array

[...'hello']  //

The result is:

6. Convert the class array into a real array and remove duplicates

[...new Set([1,2,3,3])] //

new Set returns a class array,...Convert the class array into a real array

7. Expansion algorithm

let map = new Map([  
      [1, 'one'],  
       [2, 'two'],  
       [3, 'three'],  
]);  
let arr = [...map.keys()]; // [1, 2, 3]

When writing a vue project, since you don’t know how many params there are, you can directly params:param.data or params: {undefined

...param.data}
return axios({
　　method: param.type,
　　url: value.prefix + param.url + value.postfix,
       params: {
　　    ...param.data  // 将数组展开
       }
})

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