Generate Key Javascript Map Array

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What's the best way to store a key=value array in javascript, and how can that be looped through? The key of each element should be a tag. This could be bypassed by using map = Object.create(null) since ES5, but was seldomly done. The keys of an Object are Strings and Symbols, where they can be any value for a Map. Map in JavaScript In this article we would be discussing Map object provided by ES6. Map is a collection of elements where each element is stored as a Key, value pair. Transforming Arrays with Array#map. Originally published in the A Drip of JavaScript newsletter. One of the most common tasks that developers perform in any language is taking an array of values and transforming those values. Up until recently, doing that in JavaScript took a fair bit of boilerplate code. Jun 15, 2018  It simply loops through the array (or any iterable, really) from 0 to length and creates a new index key in the enclosing array with the value returned from the spreading array at the current index. Since JavaScript returns undefined from our spreading array at each of its indices (remember, it does this by default because it doesn’t have the. Object.keys, values, entries. For plain objects, the following methods are available: Object.keys(obj) – returns an array of keys. Object.values(obj) – returns an array of values. Object.entries(obj) – returns an array of key, value pairs. Please note the distinctions (compared to map for example). Sep 14, 2017  In this article we would be discussing Map object provided by ES6.Map is a collection of elements where each element is stored as a Key, value pair. Map object can hold both objects and primitive values as either key or value. When we iterate over the map object it returns the key,value pair in the same order as inserted. Sep 24, 2018 We want to get an array of objects that have both id and name properties because the select options display better in the format of id — name than in the format of id or name only. This can be done in two steps: first, we generate an array of distinct ids; then we map the array of ids to the desired objects array. The code snippet is as follows.

  1. Generate Key Javascript Map Array Example
  2. Generate Key Javascript Map Array To String
  3. Javascript Map Array Keys

Hey everyone i'm currently learning more about javascript and wanted to know how to do something like this in PHP which is a multidimensional array with key pairs

But how would i do something like this in javascript this is what i have attempted and so far only got errors i'm using an object rather than array if i'm going about this wrong please tell me haha

Why do you try to make an Object? In Object JS doing it other way(with ':' and ',')

Butif you need a multidimensional array do this way:

Would i just access the variables in the array like

Hi Tunde,

Since an array is an object in javascript, would something like this suit you?

You can access each property either like this: multiarray.cat.name or if you prefer it to be like php: multiarray['cat']['legs']

Oh, I see! What you calling array is collection indeed. To access it like hotels['hilton']['name'] you need such object:

So, the solution to keep this data you need is:

Your awesome haha sorry i thought it was called the same in js but thats exactly what i'm looking for are there any methods to add new items into the collection ?

Try to make it this way:

Awesome that works thanks for all your help mate :D

These are commonly known as Object Literals in JavaScript but yes they are indeed associative arrays since the indexes are named (with a string) and not a numeric index.

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JavaScript arrays are used to store multiple values in a single variable.

Example

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What is an Array?

An array is a special variable, which can hold more than one value at a time.

If you have a list of items (a list of car names, for example), storing the cars in single variables could look like this:

var car1 = 'Saab';
var car2 = 'Volvo';
var car3 = 'BMW';

However, what if you want to loop through the cars and find a specific one? And what if you had not 3 cars, but 300?

The solution is an array!

An array can hold many values under a single name, and you can access the values by referring to an index number.

Creating an Array

Using an array literal is the easiest way to create a JavaScript Array.

Syntax:

Example

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Spaces and line breaks are not important. A declaration can span multiple lines:

Example

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Using the JavaScript Keyword new

The following example also creates an Array, and assigns values to it:

Example

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The two examples above do exactly the same. There is no need to use new Array().
For simplicity, readability and execution speed, use the first one (the array literal method).

Access the Elements of an Array

You access an array element by referring to the index number. Microsoft office 2008 key generator.

This statement accesses the value of the first element in cars:

Example

var cars = ['Saab', 'Volvo', 'BMW'];
document.getElementById('demo').innerHTML = cars[0];
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Note: Array indexes start with 0.

[0] is the first element. [1] is the second element.

Changing an Array Element

This statement changes the value of the first element in cars:

Example

var cars = ['Saab', 'Volvo', 'BMW'];
cars[0] = 'Opel';
document.getElementById('demo').innerHTML = cars[0];
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Access the Full Array

With JavaScript, the full array can be accessed by referring to the array name: Avs video editor 7.5 activation key generator.

Example

var cars = ['Saab', 'Volvo', 'BMW'];
document.getElementById('demo').innerHTML = cars;
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Arrays are Objects

Arrays are a special type of objects. The typeof operator in JavaScript returns 'object' for arrays.

But, JavaScript arrays are best described as arrays.

Arrays use numbers to access its 'elements'. In this example, person[0] returns John:

Array:

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Objects use names to access its 'members'. In this example, person.firstName returns John:

Object:

var person = {firstName:'John', lastName:'Doe', age:46};
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Array Elements Can Be Objects

JavaScript variables can be objects. Arrays are special kinds of objects.

Because of this, you can have variables of different types in the same Array.

You can have objects in an Array. You can have functions in an Array. You can have arrays in an Array:

myArray[0] = Date.now;
myArray[1] = myFunction;
myArray[2] = myCars;

Array Properties and Methods

The real strength of JavaScript arrays are the built-in array properties and methods:

Examples

var x = cars.length; // The length property returns the number of elements
var y = cars.sort(); // The sort() method sorts arrays

Array methods are covered in the next chapters.

The length Property

The length property of an array returns the length of an array (the number of array elements).

Example

var fruits = ['Banana', 'Orange', 'Apple', 'Mango'];
fruits.length; // the length of fruits is 4
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The length property is always one more than the highest array index.

Accessing the First Array Element

Example

fruits = ['Banana', 'Orange', 'Apple', 'Mango'];
var first = fruits[0];
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Accessing the Last Array Element

Example

fruits = ['Banana', 'Orange', 'Apple', 'Mango'];
var last = fruits[fruits.length - 1];
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Looping Array Elements

The safest way to loop through an array, is using a for loop:

Example

var fruits, text, fLen, i;
fruits = ['Banana', 'Orange', 'Apple', 'Mango'];
fLen = fruits.length;
text = '<ul>';
for (i = 0; i < fLen; i++) {
text += '<li>' + fruits[i] + '</li>';
}
text += '</ul>';
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You can also use the Array.forEach() function:

Example

var fruits, text;
fruits = ['Banana', 'Orange', 'Apple', 'Mango'];
text = '<ul>';
fruits.forEach(myFunction);
text += '</ul>';
function myFunction(value) {
text += '<li>' + value + '</li>';
}
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Adding Array Elements

The easiest way to add a new element to an array is using the push() method:

Example

var fruits = ['Banana', 'Orange', 'Apple', 'Mango'];
fruits.push('Lemon'); // adds a new element (Lemon) to fruits
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New element can also be added to an array using the length property:

Example

var fruits = ['Banana', 'Orange', 'Apple', 'Mango'];
fruits[fruits.length] = 'Lemon'; // adds a new element (Lemon) to fruits
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WARNING !

Adding elements with high indexes can create undefined 'holes' in an array:

Example

var fruits = ['Banana', 'Orange', 'Apple', 'Mango'];
fruits[6] = 'Lemon'; // adds a new element (Lemon) to fruits
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Associative Arrays

Many programming languages support arrays with named indexes.

Arrays with named indexes are called associative arrays (or hashes).

JavaScript does not support arrays with named indexes.

In JavaScript, arrays always use numbered indexes.

Example

var person = [];
person[0] = 'John';
person[1] = 'Doe';
person[2] = 46;
var x = person.length; // person.length will return 3
var y = person[0]; // person[0] will return 'John'
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WARNING !!
If you use named indexes, JavaScript will redefine the array to a standard object.
After that, some array methods and properties will produce incorrect results.

Example:

var person = [];
person['firstName'] = 'John';
person['lastName'] = 'Doe';
person['age'] = 46;
var x = person.length; // person.length will return 0
var y = person[0]; // person[0] will return undefined
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The Difference Between Arrays and Objects

In JavaScript, arrays use numbered indexes.

In JavaScript, objects use named indexes.

Arrays are a special kind of objects, with numbered indexes.

When to Use Arrays. When to use Objects.

  • JavaScript does not support associative arrays.
  • You should use objects when you want the element names to be strings (text).
  • You should use arrays when you want the element names to be numbers.

Avoid new Array()

There is no need to use the JavaScript's built-in array constructor new Array().

Use [] instead.

These two different statements both create a new empty array named points:

var points = new Array(); // Bad
var points = []; // Good

These two different statements both create a new array containing 6 numbers:

var points = new Array(40, 100, 1, 5, 25, 10); // Bad
var points = [40, 100, 1, 5, 25, 10]; // Good
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The new keyword only complicates the code. It can also produce some unexpected results:

var points = new Array(40, 100); // Creates an array with two elements (40 and 100)

What if I remove one of the elements?

var points = new Array(40); // Creates an array with 40 undefined elements !!!!!
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How to Recognize an Array

A common question is: How do I know if a variable is an array?

The problem is that the JavaScript operator typeof returns 'object':

var fruits = ['Banana', 'Orange', 'Apple', 'Mango'];
typeof fruits; // returns object
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The typeof operator returns object because a JavaScript array is an object.

Solution 1:

To solve this problem ECMAScript 5 defines a new method Array.isArray():

The problem with this solution is that ECMAScript 5 is not supported in older browsers.

Solution 2:

To solve this problem you can create your own isArray() function:

function isArray(x) {
return x.constructor.toString().indexOf('Array') > -1;
}

Generate Key Javascript Map Array Example

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Generate Key Javascript Map Array To String

The function above always returns true if the argument is an array.

Or more precisely: it returns true if the object prototype contains the word 'Array'.

Solution 3:

The instanceof operator returns true if an object is created by a given constructor:

var fruits = ['Banana', 'Orange', 'Apple', 'Mango'];
fruits instanceof Array; // returns true

Javascript Map Array Keys

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