I have recently seen some references that explain Strings in Javascript as a primitive type.I know that a primitive is a data type that is composed of no other data types and can not be broken down any further.But the problem is I have also read strings are objects.How it can be both ?Please clarify me about the confusion.
You can read about that exact topic on MDN:
Note that JavaScript distinguishes between String objects and
primitive string values. (The same is true of booleans and numbers.)
String literals (denoted by double or single quotes) and strings
returned from String calls in a non-constructor context (i.e., without
using the new keyword) are primitive strings. JavaScript automatically
converts primitives to String objects, so that it's possible to use
String object methods for primitive strings. In contexts where a
method is to be invoked on a primitive string or a property lookup
occurs, JavaScript will automatically wrap the string primitive and
call the method or perform the property lookup.
https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/String
Related
In Kyle Simpson's book You Don't Know JS: this & Object Prototypes, he writes this on the subject of how to duplicate an object:
One subset solution is that objects which are JSON-safe (that is, can be serialized to a JSON string and then re-parsed to an object with the same structure and values) can easily be duplicated with:
var newObj = JSON.parse( JSON.stringify( someObj ) );
Of course, that requires you to ensure your object is JSON safe. For some situations, that's trivial. For others, it's insufficient.
What is a "JSON-safe" object? I ran a few tests with JavaScript and so far most things (arrays, numbers, strings, objects) can be duplicated using the above line, except for methods (foo.bar), when trying to duplicate a method, undefined is inserted in the method's place in the duplicated object.
To get foo<=> JSON.parse(JSON.stringify(foo)) as true, we must be able to represent foo in the JSON format.
JSON only supports:
Number: a signed decimal number that may contain a fractional part and may use exponential E notation, but cannot include non-numbers like NaN. The format makes no distinction between integer and floating-point. JavaScript uses a double-precision floating-point format for all its numeric values, but other languages implementing JSON may encode numbers differently.
String: a sequence of zero or more Unicodecharacters. Strings are delimited with double-quotation marks and support a backslash escaping syntax.
Boolean: either of the values true or false
Array: an ordered list of zero or more values, each of which may be of any type. Arrays use square bracket notation with elements being comma-separated.
Object: an unordered collection of name/value pairs where the names (also called keys) are strings. Since objects are intended to represent associative arrays,[12] it is recommended, though not required,[13] that each key is unique within an object. Objects are delimited with curly brackets and use commas to separate each pair, while within each pair the colon ':' character separates the key or name from its value.
null: An empty value, using the word null
In javascript, the concept of JSON safe object basically refers to a javascript object that can be represented in the JSON format without any loss.
The MDN page on Array#slice states:
For strings, numbers and booleans (not String, Number and Boolean
objects), slice copies the values into the new array. Changes to the
string, number or boolean in one array do not affect the other array.
Surely string literals, being reference types (admittedly with a value semantic), are not copied. Instead a reference is copied?
String literals produce immutable primitive values. Those are not reference values.
That strings might be implemented with shared references to character arrays in JS engines is just that, an implementation detail. As you say yourself, strings do have value semantics in JS, and that's all what matters.
No, string literals are considered primitive types in JavaScript, just like numbers.
See MDN - Strings # Distinction between string primitives and String objects
Is there an upper limit to the possible character length of strings in JavaScript, and ES6+ in particular?
Could you do this?
const wowThisIsALongString = `${collectedWorksOfWilliamShakespeare}`
[I'd write the collected works out by hand but am feeling lazy.]
If I understand correctly (and odds are that I don't), a JavaScript string is just a special kind of JavaScript Object, so there's technically no limit?
But maybe things are different in practice?
EDIT / UPDATE: As people have noted, a string primitive isn't an Object. I'd never thought of it as such until I checked the ECMAScript 2015 specs.
4.3.17 String value
primitive value that is a finite ordered sequence of zero or more
16-bit unsigned integer
NOTE A String value is a member of the String type. Each integer value
in the sequence usually represents a single 16-bit unit of UTF-16
text. However, ECMAScript does not place any restrictions or
requirements on the values except that they must be 16-bit unsigned
integers.
4.3.18 String type
set of all possible String values
4.3.19 String object
member of the Object type that is an instance of the standard built-in
String constructor
NOTE A String object is created by using the String constructor in a
new expression, supplying a String value as an argument. The resulting
object has an internal slot whose value is the String value. A String
object can be coerced to a String value by calling the String
constructor as a function (21.1.1.1).
So, when they write that, is the meaning that String objects are objects which contain strings, or ... something else?
Another Update: I think that Ryan has answered this below.
There is a specified length of 253 − 1 in Section 6.1.4:
The String type is the set of all ordered sequences of zero or more 16-bit unsigned integer values (“elements”) up to a maximum length of 253-1 elements.
This is the highest integer with unambiguous representation as a JavaScript number:
> 2**53 === 2**53 - 1
false
> 2**53 === 2**53 + 1
true
Individual engines can have smaller limits. V8, for example, limits its strings to 228 − 14 characters.
Side note: primitive strings aren’t objects, but that doesn’t have much to do with length limits. JavaScript has a “primitive wrapper” misfeature allowing strings, numbers, and booleans to be wrapped by objects, and that’s what the section you linked refers to, but there’s no reason to ever use it.
This question already has answers here:
What is the difference between string primitives and String objects in JavaScript?
(12 answers)
Closed 7 years ago.
I'm reading about the difference between String literal and String objects. See
What is the difference between string literals and String objects in JavaScript?
But I'm a bit confuse because there it's explained that you can use methods of the String Objects but technically is a String literal an String Object? I'm not asking if we can use the same methods, only if a String literal is an object. Thanks!
The term "string literal" refers to a syntactic convention for representing string values directly in code.
The code
"Hello Everyone"
is a string literal for a string with 14 characters.
The value represented by a string literal is a string primitive. It is not an object. That's why if you use:
typeof "Hello Everyone"
this will return the value "string", not "object".
JavaScript allows boxing of any string primitive to promote them to string objects under certain circumstances. Attempting to call a method on a string value is one of these circumstances. So if you call:
"Hello Everyone".toUpperCase()
the value represented by this literal will be boxed into a string Object, and the method will be called on that object.
You can check the type of a Javascript variable with the typeof operator. typeof "Hello World" and typeof String("Hello World") both return the type "string".
Also, a strict-equal check "Hello" === String("Hello") returns true, which means that they are not just value-equal but type-equal.
However, typeof new String("Hello World") returns "object".
What are JavaScript Data Types?
There's
Numbers
Strings
Booleans
Objects
null
undefined
Note that there isn't a separate Integer, just number - which is represented as a double precision floating point number.
There's also
Functions
Arrays
RegExps
all of which are Objects deep down, but with enough special wiring to be mentioned on their own.
There are five primitive data types in JavaScript:
number
string
boolean
undefined
null
Everything that is not a primitive is an object.
Javascript has a typeof operator that returns a string that names the datatype of its argument. So, you could say that the datatypes in Javascript are all the possible return values of this operator. Look here:
https://developer.mozilla.org/en/JavaScript/Reference/Operators/typeof