Objects

Syntax

• object = { }
• object = new Object()
• object = Object.create(prototype[, propertiesObject])
• object.key = value
• object[“key”] = value
• object[Symbol()] = value
• object = { key1: value1, “key2”: value2, ‘key3’: value3 }
• object = { conciseMethod() { … } }
• object = { [computed() + “key”]: value }
• Object.defineProperty(obj, propertyName, propertyDescriptor)
• property_desc = Object.getOwnPropertyDescriptor(obj, propertyName)
• Object.freeze(obj)
• Object.seal(obj)

Parameters

Objects are collections of key-value pairs, or properties. The keys can be Strings or Symbols, and values are either primitives (numbers, strings, symbols) or references to other objects.

In JavaScript, a significant amount of values are objects (e.g. functions, arrays) or primitives that behave as immutable objects (numbers, strings, booleans). Their properties or their prototype’s properties can be accessed using dot (obj.prop) or bracket (obj['prop']) notation. Notable exceptions are the special values undefined and null.

Objects are held by reference in JavaScript, not by value. This means that when copied or passed as arguments to functions, the “copy” and the original are references to the same object, and a change to one’s properties will change the same property of the other. This does not apply to primitives, which are immutable and passed by value.