JavaScript Learning notes Finishing Day5

#数组
# #一: definition of an array
1. An array is an ordered set of values
2. Each value is called an element
3. Each element has a position in the array, expressed as a number, called an index. The index starts at 0.
# #二: Features
1. The elements of an array can be of any type.
2. Array index starting from 0, max 2^32-2 4,294,967,294 elements
# #三: Creating an array
1. Using array direct amount []
var arr=[1,2,3];
2. Using constructors
var arr = new Array (10); 10 Elements of Su
var arr = new Array (' A ', ' B ', ' C ');
# #四: The length of the array
Arr.length;
The Length property evaluates only the index of a nonnegative integer
# #五: Access and modification of array elements
1. Use []
2. String of numeric types can also access array elements

# #六: Sparse Array
(sparse arrays are arrays of discontinuous indexes)
1. var arr = new Array (3); --is a sparse array
2. var arr = [,,]; --is a sparse array
3. var arr = [1,2];arr[10]=100; --is a sparse array
4. Delete an element using Delete to get a sparse array
# #七数组元素的添加
1. Assign a value arr[4]=2 to the new index;
2. Insert the new element arr[arr.length]=5 at the end of the array using the array length;
3. Push () adds a new element Arr.push (' abc ') at the tail;
4. Unshift () Add a new element Arr.unshift (' abc ') at the front;
# #八: Deletion of arrays
1. Delete an element after the array delete () is not recommended--produces a sparse array
2. Pop () Delete the last element of the array arr.pop ();
3. Shift () Delete the first element of the array arr.shift ();
# #九: Determine if an array
typeof []; Unable to judge
ESMA5 defines a new method used to determine whether an array: Array.isarray ([]);
# #十: Whether the search array has elements
Arr.indexof ();
If there is a return element position
If there is no return-1
# #十一: Array traversal:
1. Use for loop traversal
for (var i = 0; I < arr.length;i++) {
Console.log (Arr[i]);
}

2. Using the for/in loop
for (var i in arr) {
Console.log (Arr[i]);
}
3. Note: The difference between traversing a sparse array and a special subscript array </font>
4. Use foreach (); Incoming anonymous function
> <font color= "Pink" > Low version IE does not support </font>



# #十二: Array of methods:
1. Join () to stitch the elements of an array into a string
var message = Arr.join (', ');
2. Concat () merging multiple arrays
var message = Arr.concat ([12,43],[4,35,3]);
var message = Arr.concat (n/a);
var message = Arr.concat (1,2,[4,,5,[6,,7]]);
3. Slice () intercepts a portion of the array (without destroying the original array) and returns the new number
var arr = List.slice (2); Remove all elements from subscript 2 to the back
var arr = list.slice (2,4); Remove elements from subscript 2 to subscript 4 (4 not included) >
4. Splice () Delete, replace, add, destroy the original array to return deleted content
var New_arr = List.splice (2); Elements after subscript 2
var New_arr = List.splice (2,2); Two elements after subscript 2
4.1 Adding a new element at the specified location
var arr = [3,454,435,343];
Arr.splice (2,0, ' abc ');
Add an ABC in front of the 435 position
4.2 Replace the element at the specified position
var arr=[1,2,3,4];arr.splice (2,1, ' abc ');
Replace 3 with ABC;
5. Reverse () array inversion change the original array

6. Sort (); Array ordering, you must use the sort function list=[1,334,32,324];
List.sort (function (A, b) {return-A;});
7. ToString () converts an array to a string

8. toLocaleString () converts an array to a local string (not commonly used)

JavaScript Learning notes Finishing Day5