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This article focuses on "what are the ways to use extension operators in JS". Interested friends may wish to take a look. The method introduced in this paper is simple, fast and practical. Let's let the editor take you to learn what are the ways to use extension operators in JS.

Copy array

We can use the expand operator to copy the array, but note that this is a shallow copy.

Const arr1 = [1JI 2jue 3]; const arr2 = [... arr1]; console.log (arr2); / / [1JI 2Jue 3]

This allows us to copy a basic array, which does not apply to multi-level arrays or arrays with dates or functions.

Merge array

Suppose we have two arrays that we want to merge into one. Earlier we could use the concat method, but now we can use the expansion operator:

Const arr1 = [1Jing 2jue 3]; const arr2 = [4je 5je 6]; const arr3 = [... arr1,... arr2]; console.log (arr3); / / [1Jing 2je 3,4je 5je 6]

We can also use different arrangements to show which should appear first.

Const arr3 = [... arr2,... arr1]; console.log (arr3); [4, 5, 6, 1, 2, 3]

In addition, the expansion operation symbol also applies to the merging of multiple arrays:

Const output = [... arr1,... arr2,... arr3,... arr4]

Add elements to the array

Let arr1 = ['this',' is', 'an']; arr1 = [... arr1,' array']; console.log (arr1); / / ['this',' is', 'an',' array']

Add attributes to an object

Suppose you have an object of user, but it lacks an age attribute.

Const user = {firstname: 'Chris', lastname:' Bongers'}

To add age to the user object, we can use the expansion operator again.

Const output = {... user, age: 31}

Use the Math () function

Suppose we have an array of numbers, and we want to get the maximum, minimum, or sum of these numbers.

Const arr1 = [1,-1, 0, 5, 3]

To get the minimum, we can use the unfold operator and the Math.min method.

Const arr1 = [1,-1, 0, 5, 3]; const min = Math.min (.arr1); console.log (min); / /-1

Similarly, to get the maximum value, you can do this:

Const arr1 = [1,-1,0,5,3]; const max = Math.max (.arr1); console.log (max); / / 5

As you can see, the maximum value is 5. If we delete 5, it will return 3.

You may wonder what happens if we don't use the unfold operator.

Const arr1 = [1,-1, 0, 5, 3]; const max = Math.max (arr1); console.log (max); / / NaN

This returns NaN because JavaScript does not know what the maximum value of the array is.

Rest parameter

Suppose we have a function that takes three parameters.

Const myFunc (x1, x2, x3) = > {console.log (x1); console.log (x2); console.log (x3);}

We can call this function in the following ways:

MyFunc (1,2,3)

But what happens if we pass an array.

Const arr1 = [1,2,3]

We can use the expansion operator to extend this array to our function.

MyFunc (.arr1); / / 1 / 2 / 3

Here, we divide the array into three separate parameters, which are then passed to the function.

Const myFunc = (x1, x2, x3) = > {console.log (x1); console.log (x2); console.log (x3);}; const arr1 = [1,2,3]; myFunc (.arr1); / / 1 / / 2 / / 3

Pass infinite parameters to the function

Suppose we have a function that takes an infinite number of parameters, as follows:

Const myFunc = (... args) = > {console.log (args);}

If we call this function with multiple arguments now, we will see the following:

MyFunc (1, 'a', new Date ())

Return:

[1, 'asides, Date {_ _ proto__: Date {}}]

We can then loop through the parameters dynamically.

Convert nodeList to an array

Suppose we used the expansion operator to get all the div on the page:

Const el = [... document.querySelectorAll ('div')]; console.log (el); / / (3) [div, div, div]

You can see here that we got three div from dom.

Now we can easily traverse these elements because they are arrays.

Const el = [... document.querySelectorAll ('div')]; el.forEach (item = > {console.log (item);}); /

Deconstruct object

Suppose we have an object, user:

Const user = {firstname: 'Chris', lastname:' Bongers', age: 31}

Now we can use the expansion operator to decompose it into a single variable.

Const {firstname,... rest} = user; console.log (firstname); console.log (rest); / / 'Chris' / / {lastname:' Bongers', age: 31}

Here, we deconstruct the user object and deconstruct firstname into firstname variables and the rest of the object into rest variables.

Expand string

The last use case of the expansion operator is to decompose a string into a single word.

Suppose we have the following string:

Const str = 'Hello'

Then, if we use the expansion operator on this string, we get an array of letters.

Const str = 'Hello'; const arr = [... str]; console.log (arr); / / [' hashing, 'eBay,' lumped, 'lumped,' o'] so far, I believe you have a deeper understanding of "what are the ways to use extension operators in JS". You might as well do it in practice! Here is the website, more related content can enter the relevant channels to inquire, follow us, continue to learn!

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