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In ES6, you can use the reverse() method of the array object to achieve array reversal. This method is used to reverse the order of the elements in the array, putting the last element first, and the first The element is placed at the end, the syntax is "array.reverse()". The reverse() method will modify the original array. If you do not want to modify it, you need to use it with the expansion operator "...", and the syntax is "[...array].reverse()".
The operating environment of this tutorial: Windows 7 system, ECMAScript version 6, Dell G3 computer.
Reversing an array with specific constraints is one of the most common challenges in job interviews and coding tests.
In ES6, you can use the reverse() method of the array object to reverse the array. The reverse() method reverses the order of the array elements so that the first element becomes the last element and the last element becomes the first element.
let numbers = [1, 2, 3, 4, 5]; let reversedNumbers = numbers.reverse(); console.log(reversedNumbers); // [5, 4, 3, 2, 1]
But remember, the reverse
method modifies the original array:
let numbers = [1, 2, 3, 4, 5]; let reversedNumbers = numbers.reverse(); console.log(reversedNumbers); // [5, 4, 3, 2, 1] console.log(numbers); // [5, 4, 3, 2, 1]
Some coding challenges may want you to keep the original array, so let's look at how to reverse an array without changing the original array.
You can use the spread operator (Spread) in combination with the reverse
method to reverse Convert an array without changing the original array.
First, place the elements returned by the spread operator into a new array by surrounding the spread syntax with square brackets []
:
[...numbers]
Then, you add Call the reverse
method on. This way, the reverse
method will be executed on the new array instead of the original array:
let numbers = [1, 2, 3, 4, 5]; let reversedNumbers = [...numbers].reverse(); console.log(reversedNumbers); // [5, 4, 3, 2, 1] console.log(numbers); // [1, 2, 3, 4, 5]
Note: The
spread
method is ES6 syntax , when you need to support older browsers or want to use ES5 syntax, you can use theslice
andreverse
methods together. Let's see now.
slice
method is used to get the selected elements as a new array Returns, when you call the method without any parameters, it will return a new array that is identical to the original array (from first element to last element).
Next, you call the reverse
method on the newly returned array, which is why the original array is not reversed:
let numbers = [1, 2, 3, 4, 5]; let reversedNumbers = numbers.slice().reverse(); console.log(reversedNumbers); // [5, 4, 3, 2, 1] console.log(numbers); // [1, 2, 3, 4, 5]
Sometimes interviews challenge you to reverse the array without using reverse
method. no problem! You can use a combination of a for
loop and an array's push
method, like in the example below.
let numbers = [1, 2, 3, 4, 5]; let reversedNumbers = []; for(let i = numbers.length -1; i >= 0; i--) { reversedNumbers.push(numbers[i]); } console.log(reversedNumbers);
Finally, let's say you are tasked with writing your own reverse function that needs to reverse an array without creating a copy. At first glance, this may seem complicated, but don't worry because it's actually quite simple.
What you need to do here is swap the first and last elements of the array, then the second and second-to-last elements, and so on until all elements are swapped.
Let's write a function to do this.
Write function customReverse
and use array.length - 1
as a variable, while storing the first index as 0
and the last index .
function customReverse(originalArray) { let leftIndex = 0; let rightIndex = originalArray.length - 1; }
Next, create a while
loop that will run as long as leftIndex
is less than rightIndex
.
Within this loop, swap the values of leftIndex
and rightIndex
, you can temporarily store one of the values in a temporary variable:
while (leftIndex < rightIndex) { // 交换元素 let temp = originalArray[leftIndex]; originalArray[leftIndex] = originalArray[rightIndex]; originalArray[rightIndex] = temp; }
Finally, leftIndex
is moved up, rightIndex
is moved down, and when the while
loop repeats, it swaps the second-to-last element, and so on:
function customReverse(originalArray) { let leftIndex = 0; let rightIndex = originalArray.length - 1; while (leftIndex < rightIndex) { // 用temp变量交换元素 let temp = originalArray[leftIndex]; originalArray[leftIndex] = originalArray[rightIndex]; originalArray[rightIndex] = temp; // 将索引移到中间 leftIndex++; rightIndex--; } }
The loop will stop immediately when there are no more elements to reverse. For odd-numbered arrays, the values of leftIndex
and rightIndex
will be equal, so there is no need to exchange them. For an array of even numbers leftIndex
will be greater than rightIndex
.
You can test the feature to see if it works properly, as shown below:
let myArray = [1, 2, 3, 4, 5]; customReverse(myArray); console.log(myArray); // output is [5, 4, 3, 2, 1]
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