Hướng dẫn javascript push 2d array
Iterating over two dimensions means you'll need to check over two dimensions. Show
assuming you're starting with:
You want to expand this two-dimensional array to become:
Which means you need to understand what the difference is. Start with the outer array:
If you want to make this array longer, you need to check that it's the correct length, and add more inner arrays to make up the difference:
The next step requires iterating over every column in every array, we'll build on the original code: In JavaScript, arrays aren't primitives but are instead Constructor
Creates a new Static properties
Returns the Static methods
Creates a new Array.isArray() Returns Array.of() Creates a new Instance properties
Reflects the number of elements in an array. Array.prototype[@@unscopables] Contains property names that were not included in the ECMAScript standard prior to the ES2015 version and that are ignored for Instance methods
Returns the array item at the given index. Accepts negative integers, which count back from the last item. Array.prototype.concat() Returns a new array that is the calling array joined with other array(s) and/or value(s). Array.prototype.copyWithin() Copies a sequence of array elements within an array. Array.prototype.entries() Returns a new array iterator object that contains the key/value pairs for each index in an array. Array.prototype.every() Returns Array.prototype.fill() Fills all the elements of an array from a start index to an end index with a static value. Array.prototype.filter() Returns a new array containing all elements of the
calling array for which the provided filtering function returns Array.prototype.find() Returns the value of the first element in the array that satisfies the provided testing function, or Array.prototype.findIndex() Returns the index of the first element in the array that satisfies the provided testing function, or Array.prototype.findLast() Returns the value of
the last element in the array that satisfies the provided testing function, or Array.prototype.findLastIndex() Returns the index of the last element in the array that satisfies the provided testing function, or Array.prototype.flat() Returns a new array with all sub-array elements concatenated into it recursively up to the specified depth. Array.prototype.flatMap() Returns a new array formed by applying a given callback function to each element of the calling array, and then flattening the result by one level. Array.prototype.forEach() Calls a function for each element in the calling array. Array.prototype.group() ExperimentalGroups the elements of an array into an object according to the strings returned by a test function. Array.prototype.groupToMap() ExperimentalGroups the elements of an array into a Array.prototype.includes() Determines whether the calling array contains a value, returning Array.prototype.indexOf() Returns the first (least) index at which a given element can be found in the calling array. Array.prototype.join() Joins all elements of an array into a string. Array.prototype.keys() Returns a new array iterator that contains the keys for each index in the calling array. Array.prototype.lastIndexOf() Returns the last (greatest) index at which a given element can be found in the calling array, or Array.prototype.map() Returns a new array containing the results of invoking a function on every element in the calling array. Array.prototype.pop() Removes the last element from an array and returns that element. Array.prototype.push() Adds one or more elements to the end of an array, and returns the new Array.prototype.reduce()
Executes a user-supplied "reducer" callback function on each element of the array (from left to right), to reduce it to a single value. Array.prototype.reduceRight() Executes a user-supplied "reducer" callback function on each element of the array (from right to left), to reduce it to a single value. Array.prototype.reverse() Reverses the order of the elements of an array in place. (First becomes the last, last becomes first.) Array.prototype.shift() Removes the first element from an array and returns that element. Array.prototype.slice() Extracts a section of the calling array and returns a new array. Array.prototype.some() Returns Array.prototype.sort() Sorts the elements of an array in place and returns the array. Array.prototype.splice() Adds and/or removes elements from an array. Array.prototype.toLocaleString() Returns a localized string representing the calling array and its elements. Overrides the Array.prototype.toString() Returns a string representing the calling array and its elements. Overrides the Array.prototype.unshift() Adds one or more elements to the front of an array, and returns the new Array.prototype.values() Returns a new array iterator object that contains the values for each index in the array. Array.prototype[@@iterator]() An alias for the
ExamplesThis section provides some examples of common array operations in JavaScript. Create an arrayThis example shows three ways to create new array: first using array literal
notation, then using the
Create a string from an arrayThis example uses the
Access an array item by its indexThis example shows how to access items in the
Find the index of an item in an arrayThis example uses the
Check if an array contains a certain itemThis example shows two ways to check if the
Append an item to an arrayThis example uses the
Remove the last item from an arrayThis example uses the
Note: Remove multiple items from the end of an arrayThis example uses the
Truncate an array down to just its first N itemsThis example uses the
Remove the first item from an arrayThis example uses the
Note:
Remove multiple items from the beginning of an arrayThis example uses the
Add a new first item to an arrayThis example uses the
Remove a single item by indexThis example uses the
Remove multiple items by indexThis example uses the
Replace multiple items in an arrayThis example uses the
Iterate over an arrayThis example uses a
But Call a function on each element in an arrayThis example uses the
Merge multiple arrays togetherThis example uses the
Copy an arrayThis example shows three ways to create a new array from the existing
All built-in array-copy operations (spread syntax,
You can also create deep copies using the Finally, it's important to understand that assigning an existing array to a new variable doesn't create a copy of either the array or its elements. Instead the new variable is just a reference, or alias, to the original array; that is, the original array's name and the new variable name are just two names for the exact same object (and so will always evaluate as strictly equivalent). Therefore, if you make any changes at all either to the value of the original array or to the value of the new variable, the other will change, too:
Grouping the elements of an arrayThe Here we have a simple inventory array that contains "food" objects that have a
To use The code below uses a arrow function to return the
Note that the returned object references the same elements as the original array (not deep copies). Changing the internal structure of these elements will be reflected in both the original array and the returned object. If you can't use a string as the key, for example, if the information to group is associated with an object that might change, then you can instead use
Other examplesCreating a two-dimensional arrayThe following creates a chessboard as a two-dimensional array of strings. The first move is made by copying the
Here is the output: R,N,B,Q,K,B,N,R P,P,P,P,P,P,P,P , , , , , , , , , , , , , , , , , , , , , , , , , , , , p,p,p,p,p,p,p,p r,n,b,q,k,b,n,r R,N,B,Q,K,B,N,R P,P,P,P,P,P,P,P , , , , , , , , , , , , , , , , , ,p, , , , , , , , , , p,p,p,p, ,p,p,p r,n,b,q,k,b,n,r Using an array to tabulate a set of values
Results in // The first column is the index 0 1 0 1 2 2 2 4 8 3 8 18 4 16 32 5 32 50 6 64 72 7 128 98 8 256 128 9 512 162 Creating an array using the result of a matchThe result of a match between a
For example:
For more information about the result of a match, see the Notes
Array elements are object properties in the same way that
JavaScript syntax requires properties beginning with a digit to be accessed using bracket notation instead of dot notation. It's also possible to quote the array indices
(e.g., The
Only Relationship between length and numerical propertiesA JavaScript array's
Several of the built-in array methods (e.g., Other methods (e.g.,
When setting
a property on a JavaScript array when the property is a valid array index and that index is outside the current bounds of the array, the engine will update the array's
Increasing the
Decreasing the
This is explained further on the Array methods and empty slotsEmpty slots in sparse arrays behave inconsistently between array methods. Generally, the older
methods will skip empty slots, while newer ones treat them as Among methods that iterate through multiple elements, the following do an
For exactly how they treat empty slots, see the page for each method. These methods treat empty slots as if they are
Copying methods and mutating methodsSome methods do not mutate the existing array that the method was called on, but instead return a new array. They do so by first accessing
Other methods mutate the array that the method was called on, in which case their return value differs depending on the method: sometimes a reference to the same array, sometimes the length of the new array. The following methods create new arrays with
Note that The following methods mutate the original array:
Generic array methodsArray methods are always generic — they don't access any internal data of the array object. They only access the array elements through the
Specifications
Browser compatibilityBCD tables only load in the browser See also |