Array.prototype.fill() with object passes reference and not new instance

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Just a small question.

I was toying a bit and was trying to instantiate a new array of lenght x, where all elements of that array where initialized to a value y

var arr = new Array(x).fill(y);

This works well if the value of y is anything other than an object. Meaning that is y is an object, the following is true:

var arr = new Array(2).fill({});
arr[0] === arr[1]; //is true;
arr[0].test = 'string';
arr[1].test === 'string'; //is also true;

Is there any way to state that a new object should be created for each element while using the fill-function? Or should I just convert it to a loop?

Thanks in advance!

You can first fill the array with any value (e.g. undefined), and then you will be able to use map:

var arr = new Array(2).fill().map(u => ({}));
var arr = new Array(2).fill().map(Object);

Array.prototype.fill(), References & Guides The filter() method creates a new array with all elements that pass the test Array elements which do not pass the callback test are simply the value of the element; the index of the element; the Array object Array.​prototype.every() · Array.prototype.fill(); Array.prototype.filter()  Allows the addition of properties to all array objects. Methods Array.from() Creates a new Array instance from an array-like or iterable object. Array.isArray() Returns true if a variable is an array, if not false. Array.of() Creates a new Array instance with a variable number of arguments, regardless of number or type of the arguments. Array

Array.prototype.filter(), Although not recommended, you can create a new function object by passing the we have a Book constructor function that is used to create book instances. Instead it makes the new variable reference the same function object as original. function () {; var f = this;; var curryArgs =;  In simpler terms, objects are passed to methods by reference, while simple types like int and int32 are passed by value. The difference is easy to understand. The difference is easy to understand. When you pass a simple type to a method, the method gets a copy of the original variable.

One performant solution: Array.from({ length: 5 }, () => new Object())

JavaScript Function Objects, If you want to pass it explicitly, you can use a function's call method, which takes Many objects don't directly have Object.prototype as their prototype but instead Prototypes are useful for defining properties for which all instances of a class share let object = new class { getWord() { return "hello"; } }; console.log(object. Create an instance of the object with new. To define an object type, create a function for the object type that specifies its name and properties. An object can have a property that is itself another object. See the examples below. When the code new Foo() is executed, the following things happen: A new object is created, inheriting from Foo

Shortest Possable:

let node =  [...Array(2)].map(_=>({}))

The Secret Life of Objects :: Eloquent JavaScript, Uint8ClampedArray.prototype.entries(): Returns a new Array Iterator object that Tests whether all elements in the array pass the test provided by a function. Uint8ClampedArray.prototype.fill(): Fills all the elements of an array from a start if an element in the array satisfies the provided testing function or -1 if not found. Array.prototype.fill() with object passes reference and not .fill will insert the same exact object (same instance) The value in this case is an object

Ilias Karim's answer is most excellent. I just did the following:

a = Array.from({length:l}, () => new Array(c).fill(prefix));

to create a pre-filled 2D array of the specified size, l by c, filled with prefix. Now my code can fill in the slots in the 2D matrix that need non-prefix values.

javascript Uint8ClampedArray, References to objects with a lifespan longer than that of the native method Passing arguments and this to listeners; Asynchronous vs. identical but not reference equal: // // { // [Symbol()]: 1 // } const weakMap1 = new WeakMap(); returned // Buffer instance might contain old data that needs to be // overwritten using fill(),  Returns true if a variable is an array, if not false. Array.of() Creates a new Array instance with a variable number of arguments, regardless of number or type of the arguments. Array instances. All Array instances inherit from Array.prototype. The prototype object of the Array constructor can be modified to affect all Array instances. Properties

Node.js v14.2.0 Documentation, fill() (see below) is a better choice. from() in subclasses of Array #. Another use case for Array.from() is to convert an array-like or iterable object  fill is intentionally generic: it does not require that its this value be an Array object. fill is a mutator method: it will change the array itself and return it, not a copy of it. If the first parameter is an object, each slot in the array will reference that object.

ECMAScript 6's new array methods, 2.2 Example 2: Variables and Functions prompt() , confirm() 6.1 Creating an Object via Constructor and the new Operator 7.3 __proto__ and .prototype If you modify the codes and reload the web page, the new codes may not get executed getElementsByName(aName): returns an array of HTML elements having  The Int8Array typed array represents an array of twos-complement 8-bit signed integers. The contents are initialized to 0. Once established, you can reference elements in the array using the object's methods, or using standard array index syntax (that is, using bracket notation).

JavaScript Tutorial: The Basics, You can't get very far in JavaScript without dealing with objects. Now whenever we want to create a new animal (or more broadly speaking a new “instance”), all we have to do is invoke our Animal function, passing it the animal's console.log​(Array.prototype) /* concat: ƒn concat() constructor: ƒn Array()  What to remember about object references. Java always passes parameter variables by value. Object variables in Java always point to the real object in the memory heap. A mutable object’s value can be changed when it is passed to a method. An immutable object’s value cannot be changed, even if it is passed a new value.

  • also Array.from({length:2}, u => ({}))