JavaScript Array Methods
Converting Arrays to Strings
The JavaScript method toString() converts an array to a string of (comma separated) array values.
例子
const 水果 = ["香蕉", "橙子", "苹果", "芒果"];
document.getElementById("demo").innerHTML = fruits.toString();
Result:
这 join() method also joins all array elements into a string.
It behaves just like toString(), but in addition you can specify the separator:
例子
const 水果 = ["香蕉", "橙子", "苹果", "芒果"];
document.getElementById("demo").innerHTML = fruits.join(" * ");
Result:
Popping and Pushing
When you work with arrays, it is easy to remove elements and add new elements.
This is what popping and pushing is:
Popping items out of an array, or pushing items into an array.
JavaScript Array pop()
这 pop() method removes the last element from an array:
这 pop() method returns the value that was "popped out":
JavaScript Array push()
这 push() method adds a new element to an array (at the end):
这 push() method returns the new array length:
Shifting Elements
Shifting is equivalent to popping, but working on the first element instead of the last.
JavaScript Array shift()
这 shift() method removes the first array element and "shifts" all other elements to a lower index.
这 shift() method returns the value that was "shifted out":
JavaScript Array unshift()
这 unshift() method adds a new element to an array (at the beginning), and "unshifts" older elements:
这 unshift() method returns the new array length.
Changing Elements
Array elements are accessed using their 索引号:
Array indexes start with 0:
[0] is the first array element
[1] is the second
[2] is the third ...
JavaScript Array length
这 length property provides an easy way to append a new element to an array:
JavaScript Array delete()
Warning!
Array elements can be deleted using the JavaScript operator delete.
Using delete leaves undefined holes in the array.
Use pop() or shift() instead.
Merging (Concatenating) Arrays
这 concat() method creates a new array by merging (concatenating) existing arrays:
Example (Merging Two Arrays)
const myGirls = ["Cecilie", "Lone"];
const myBoys = ["Emil", "Tobias", "Linus"];
const myChildren = myGirls.concat(myBoys);
亲自尝试 »
这 concat() method does not change the existing arrays. It always returns a new array.
这 concat() method can take any number of array arguments:
Example (Merging Three Arrays)
const arr1 = ["Cecilie", "Lone"];
const arr2 = ["Emil", "Tobias", "Linus"];
const arr3 = ["Robin", "Morgan"];
const myChildren = arr1.concat(arr2, arr3);
亲自尝试 »
这 concat() method can also take strings as arguments:
Example (Merging an Array with Values)
const arr1 = ["Emil", "Tobias", "Linus"];
const myChildren = arr1.concat("Peter");
亲自尝试 »
Splicing and Slicing Arrays
这 splice() method adds new items to an array.
这 slice() method slices out a piece of an array.
JavaScript Array splice()
这 splice() method can be used to add new items to an array:
The first parameter (2) defines the position where new elements should be added (spliced in).
The second parameter (0) defines how many elements should be removed.
The rest of the parameters ("Lemon" , "Kiwi") define the new elements to be added.
这 splice() method returns an array with the deleted items:
Using splice() to Remove Elements
With clever parameter setting, you can use splice() to remove elements without leaving "holes" in the array:
The first parameter (0) defines the position where new elements should be added (spliced in).
The second parameter (1) defines how many elements should be removed.
The rest of the parameters are omitted. No new elements will be added.
JavaScript Array slice()
这 slice() method slices out a piece of an array into a new array.
This example slices out a part of an array starting from array element 1 ("Orange"):
例子
const fruits = ["Banana", "Orange", "Lemon", "Apple", "Mango"];
const citrus = fruits.slice(1);
亲自尝试 »
Note
这 slice() method creates a new array.
这 slice() method does not remove any elements from the source array.
This example slices out a part of an array starting from array element 3 ("Apple"):
例子
const fruits = ["Banana", "Orange", "Lemon", "Apple", "Mango"];
const citrus = fruits.slice(3);
亲自尝试 »
这 slice() method can take two arguments like slice(1, 3).
The method then selects elements from the start argument, and up to (but not including) the end argument.
例子
const fruits = ["Banana", "Orange", "Lemon", "Apple", "Mango"];
const citrus = fruits.slice(1, 3);
亲自尝试 »
If the end argument is omitted, like in the first examples, the slice() method slices out the rest of the array.
例子
const fruits = ["Banana", "Orange", "Lemon", "Apple", "Mango"];
const citrus = fruits.slice(2);
亲自尝试 »
Automatic toString()
JavaScript automatically converts an array to a comma separated string when a primitive value is expected.
This is always the case when you try to output an array.
These two examples will produce the same result:
例子
const 水果 = ["香蕉", "橙子", "苹果", "芒果"];
document.getElementById("demo").innerHTML = fruits.toString();
亲自尝试 »
Note
All JavaScript objects have a toString() method.
Finding Max and Min Values in an Array
There are no built-in functions for finding the highest or lowest value in a JavaScript array.
You will learn how you solve this problem in the next chapter of this tutorial.
Sorting Arrays
Sorting arrays are covered in the next chapter of this tutorial.
