JavaScript, arrays: description

JavaScript is a modern programming language, it is unique in terms of syntax and semantics. It is specific, but easy to use and effective when it comes to developing a dynamic and reliable network resource.

javascript array

JavaScript array is a modern form of data representation that differs from similar structures of other languages. Experience in presenting and processing information for JavaScript has always been essential. It is here, in the browser, that the dialogue with the client works. It is here that it is important to quickly disassemble a line of information from the server and paint it using the necessary tags. Server languages ​​form the content and structure of pages, but their proper use is the concern of the browser language.

Information Representation: Variables and Data

A professional developer uses variables in simple cases when he “does” for (...) {...}, “controls” while (...) {...}, “uses” the switch () {case "": ...}, ... structure in In all other cases, information is represented by data structures.

Sample code, author's insert, not drawing

Rarely enough, data is represented by a simple set of variables.It is a static construct that unites commonality in naming and using. Working with variable sets is limited by the amount of information provided, and is therefore used for simple algorithms and in local functions.

JavaScript array is a more dynamic and capacious version of a variable when it is a data structure. By indexing an array, for example, by value line, time, or another parameter, you can have different content for each index. An array can be a set (defined structure) of variables, which, when placed in another array, will represent the dynamics of such a structure either by parameter or by time.

Finally, you can create an array of objects or a system of objects — a conceptual combination of data that has a structure, content, and a set of methods that “themselves” exhibit the corresponding properties.

In all these cases, the information is presented in a rigid, formal and accessible manner for processing by means of the language. Only if the code itself is manipulated by the “system itself” of objects and no construction is allowed outside the method of an object, can we say that there is a chance to process and create informationnot formalized or formalized during the execution of the algorithm.

Syntactic language constructs

In the first approximation, the JavaScript array is similar to the syntactic constructs of other languages. Semantics is also equivalent, except for the forms of its expression. You can use the syntax and semantics of JavaScript and successfully solve any complex problem.

javascript associative array

There is no chance that the full mobility of the code and the adaptation of the created resource to the changing conditions of application will be achieved, an adequate response to any unforeseen change of the incoming information and the rules for its processing can be successfully accomplished.

The language syntax standard, which defines arrays, functions, and methods in JavaScript, is quite extensive, but in practice only a fraction is usually used.

Sample code, author's insert, not drawing

forEach is the most interesting array method. JavaScript provides the developer with the ability to define his own function for performing work on each element of the array. There is no concept of 'break', that is, forEach should be viewed as an operation on all elements of the array.

  • aData.forEach (function (val, ind, arr) {...});

here 'val' is the element, 'ind' is its index, and 'arr' is the actual array 'aData'. The function can perform any actions on the elements of the array.If it has a certain meaning, it will be a developer’s operation, and not a syntax of the language, that is, the array will have not only the content, but also the operations available to it according to its purpose in the general context of the algorithm.

Beyond syntax

Using an array of JavaScript objects, you can go beyond the syntax. Formally, each object variable and each construction of its method lies within the syntax of the language, but in the context of object-oriented programming, a system effect arises — a new quality that offers its own syntax: “independent” relations between objects.

The classical concept of software development: translation of a formal algorithm into concrete syntactic constructions of a language. In any place of the code there is a hard connection with what happened to this place and what will happen after it.

javascript remove array element

The object-oriented formula looks radically different. There are objects that have content and properties. That is what provides the relationship (the code that implements them) of objects with each other. No code outside of these relationships should be.

In JavaScript, the array element and access mechanism has the original context. All elements are equivalent, but the last one is special.An array is not an object, but by viewing an array through the prism of its last element, in the context of its access mechanism, you can get an object that changes its essence and properties - this is an important omission of the current (modern) concept of object-oriented programming, indirectly implemented by developers JavaScript language.

Javascript array: creation

Ideal and beautiful array construction:

  • var aData = []; // essentially always an array;
  • var aData = {}; // by content, possibly an associative array;

You can write and more "intelligently":

  • var aData = new Array ();

or very "notorious":

  • var aData = new Array (13).

JavaScript does not insist on the mandatory indication of the number of elements and does not impose any rules regarding indexing, sizes or types of elements. On this simple basis, it is not recommended to abuse their rights by limiting them: all arrays should be represented and used as freely as possible.

Using arrays

Each element of the array has an index - a numeric value from 0 to 232but should not approach this figure. A practical and pragmatic JavaScript array is dozens, hundreds, thousands of elements, but no more.If more is needed, it is better to first revise the algorithm or the technical task, and if nothing happens, then only multimillion massive structures can be designed in the depths of the browser.

javascript array length

Array indexes are not always consistent. In JavaScript, removing an array element means making a “hole” in it. In the process of using an array, it may well turn into a “sieve” of indices, which will in no way affect its performance or the safety of other elements.

JavaScript is deprived of a concise PHP construct: $ aData [] = "new element"; and suggests to rigidly indicate what is added and in which element (with what index) the value changes. Item type does not matter. An array can contain all that is allowed by the syntax, in any order and assortment.

The push () and pop () methods eliminate the lack of “$ aData [] = ...”, but draw the developer’s attention to the idea of ​​the last element and remind you of the concept of a stack. A similar pair of methods — unshift () and shift () — works with the first element of the array, shifting the other elements towards large indices.

Sample code, author's insert, not drawing

For javascript, array length is a relative concept. It does not always reflect the actual number of elements, and, being tied to the length method, for example,in the loop, you should always check whether the element with the desired index actually exists.

Array dimension

Systems are “always one-dimensional”, but every system consists of internal subsystems, and is in itself a part of something more global. Like the general concept of systems, there is no two-dimensional array in JavaScript, but it can easily be created by adding other arrays as array elements.

Sample code, author's insert, not drawing

Indexing by internal arrays is formed naturally: “aData [i] [j] ... [z]”, but the idea is always preferable:

  • var aElement = aData [i]; // select the internal array;
  • aElement [j] = ...; // use the element of the internal array.

In JavaScript, adding a variable of any type and in any order to an array is allowed. You can also add something to the internal array by the general rules. To access the elements, you can use a sequence of [] brackets, but it is always preferable to perform reassignment, limited to only one pair [] in each expression.

Multidimensional JavaScript arrays are normal, provided by the syntax and quite applicable in practice. But, as in other languages, it is best when measurements are smaller and readability of the code is higher.Programs, of course, are written for computers, for interpreters and compilers, but people write them, people accompany them too, and the higher the availability of the code for the author and the third-party developer, the more practical it is.

Add and remove items

The JavaScript syntax allows you to add elements to an array by simply creating a new index:

  • aData [3] = "some value";
  • aData [100] = "last item".

After these JavaScript statements, the aData array will have 101 elements. The numbering starts from index 0. For the length method, it does not matter how many elements there were in the array at the time of execution of “aData [100] = ...;”.

javascript array sorting

To remove an array element in JavaScript, you can use its methods pop () or shift (). In the first case, the result of var last = aInfo.pop () will be 'watermelon', and in the array will remain: 'apple', 'pear', 'mandarin'. In the second case, var first = aInfo.shift () will be 'apple', and the remaining elements will move to the beginning.

This option is very effective when the array of JavaScript objects is an object of changing semantics and content. The mechanism of sampling an element with its removal allows you to use the current element of the array and go straight to the next one. As in the stack: taken from the stack, used - and got access to the next element.

When using the JavaScript operator, you can delete the array element as follows:

  • delete aInfo [1].

After executing this statement, the element will actually remain in the array, but its value will be 'undefined'. Using the slice method, a JavaScript array can be "cut":

  • aData = aInfo.slice (0, 2).

The original aInfo array will remain unchanged, and only apple and pear will fall into aData. If you write:

  • aData = aInfo.slice (2);

then only a 'mandarin' and a 'watermelon' remain in the aData array.

Sort, string and array elements

JavaScript operations: sorting an array, converting an array to a string, forming an array from a string, and changing the order of elements are the most requested. These operations are carried out using the methods:

  • sort (sort elements),
  • join (convert array to string),
  • split (convert string to array)
  • reverse (change the order of the elements).

These are the most interesting and used tools for processing arrays and strings. An interesting feature: for JavaScript, the array element and string are a kind of complementary qualities. If you do not consider the characteristic feature of modern languages: any variable is always a string, that is, it can always be considered as a string, then transforming an array into a string and back is a very popular and effective operation.

javascript two-dimensional array

The use of the join / split pair is particularly original: the union of the elements of an array into a string occurs on one separator (often empty, that is, the elements are merged into one string), and the inverse transformation into an array is performed on another separator.

Sample code, author's insert, not drawing

If you do not take into account the implementation of the methods of merging and separation, the use of this pair allows you to create excellent algorithms.

The reverse () function is applied directly to the array and reverses the order of elements in it. The sort () function sorts the elements in the source array, returns the result sorted alphabetically.

If you pass a function as a parameter to sort (function (a, b) {...; return result;}), you can control the sort order using your own algorithm. Such a function should return '0' if 'a' and 'b' are equivalent, '-1' - if 'a' should precede 'b' and '1' - if 'b' should precede 'a'.

If there is no chance to get an incorrect result with respect to the reverse () function, then with respect to sorting, the algorithm for its execution and testing written code is essential. This is especially important to remember. when the array contains the characters (strings) of the national alphabet.

Smart arrays and own indices

For JavaScript, an associative array is the primitive form of an object. There are simply no methods, but there are only pairs of "key" and "value". To denote such an array, a pair of curly braces is used.

Sample code, author's insert, not drawing

In this example, the cSortCols array is used, the elements of which take three values:

  • '' - no sorting;
  • 'u' - sort ascending (up);
  • 'd' - sorting in descending order (down).

However, depending on what exactly is sorted (in this example, the site was designed for passenger transport on shuttle buses): passengers, carriers, buses or cities. Therefore, in the tables of elements it is allowed to sort only by specific columns. Therefore, on each specific page, the cSortCols array has specific content: cUsersSort, cCompaniesSort, cBusesSort, or cCitiesSort.

Creating an associative array in JavaScript can go much further. The given example of sorting is a particular solution of a very private task: the way out of the situation when the own JavaScript function (sort) is not applicable.

Data structures are very good, and using variable sets is very impractical. But no one forbids the use of variable names as indices. The array in which the indices are represented by variable names is a wonderful mobile data structure.It does not necessarily have all the indices, but in each place of the program they will be in the right composition.

A developer can construct smart arrays that will reflect the right data structures in the right place. At the same time, it is possible not to proceed to the full use of objects, just use their capabilities at the stage of describing the structure and content of data.

Practice working with arrays

Unlike server languages, in which it is always clear what to handle and what should be the result, JavaScript requires specific multi-level thinking. A site page can spawn script events and calls in unexpected ways. Even when the technical task for the site is done in an ideal way, and the dialogue with the visitor cannot go beyond the established limits, surprises happen.

javascript add to array

A characteristic feature of JavaScript is that the page element can activate a particular process. As a result, certain data, arrays, objects will be changed. Another process should have an idea of ​​what has been changed.

Ideally, processes should be painted on objects and arrays in such a way that, by initiating one process, any event predetermines everything that is necessary for all other processes dependent on it.

It is possible not to welcome object-oriented programming and not to strive to ensure that all pages of the site are provided with full-featured systems of objects that in themselves enter into relations with each other and there is not a single line of code outside the methods of such objects, but even in the case of an exclusively classical style of development. JavaScript arrays, especially associative and armed sets of implementations of the forEach function, are an excellent tool for reliable and practical code.

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