String

Podsumowanie

Tworzy obiekt pozwalający działać na ciągach znaków.

Składnia

Literały znakowe są postaci:

'string text'
"string text"
"中文 español English हिन्दी العربية português বাংলা русский 日本語 ਪੰਜਾਬੀ 한국어 தமிழ்"

Beside regular, printable characters, special characters can be encoded using escape notation:

Or, using the String global object directly:

String(thing)
new String(thing)

Parametry

thing

Dowolny łańcuch znaków.

Opis

trings are useful for holding data that can be represented in text form. Some of the most-used operations on strings are to check their length, to build and concatenate them using the + and += string operators, checking for the existence or location of substrings with the indexOf() method, or extracting substrings with the substring() method.

Character access

There are two ways to access an individual character in a string. The first is the charAt() method:

return 'cat'.charAt(1); // returns "a"

The other way (introduced in ECMAScript 5) is to treat the string as an array-like object, where individual characters correspond to a numerical index:

return 'cat'[1]; // returns "a"

For character access using bracket notation, attempting to delete or assign a value to these properties will not succeed. The properties involved are neither writable nor configurable. (See Object.defineProperty() for more information.)

Comparing strings

C developers have the strcmp() function for comparing strings. In JavaScript, you just use the less-than and greater-than operators:

var a = 'a';
var b = 'b';
if (a < b) { // true
  print(a + ' is less than ' + b);
} else if (a > b) {
  print(a + ' is greater than ' + b);
} else {
  print(a + ' and ' + b + ' are equal.');
}

A similar result can be achieved using the localeCompare() method inherited by String instances.

Distinction between string primitives and String objects

Note that JavaScript distinguishes between String objects and primitive string values. (The same is true of Boolean 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.

var s_prim = 'foo';
var s_obj = new String(s_prim);

console.log(typeof s_prim); // Logs "string"
console.log(typeof s_obj);  // Logs "object"

String primitives and String objects also give different results when using eval(). Primitives passed to eval are treated as source code; String objects are treated as all other objects are, by returning the object. For example:

var s1 = '2 + 2';             // creates a string primitive
var s2 = new String('2 + 2'); // creates a String object
console.log(eval(s1));        // returns the number 4
console.log(eval(s2));        // returns the string "2 + 2"

For these reasons, code may break when it encounters String objects when it expects a primitive string instead, although generally authors need not worry about the distinction.

A String object can always be converted to its primitive counterpart with the valueOf() method.

console.log(eval(s2.valueOf())); // returns the number 4

Własności

String.prototype

Pozwala na dodawanie własności do obiektu String.

Metody

String.fromCharCode()

Zwraca łańcuch znaków stworzony przez podaną sekwencję kodów Unicode.

String.fromCodePoint()

Returns a string created by using the specified sequence of code points.

String.raw()

Returns a string created from a raw template string.

Przykłady

Example: String conversion

It's possible to use String as a "safer" toString() alternative, as although it still normally calls the underlying toString(), it also works for null and undefined. For example:

var outputStrings = [];
for (var i = 0, n = inputValues.length; i < n; ++i) {
  outputStrings.push(String(inputValues[i]));
}