a) Strings

Este objeto nos permite manipular diferentes tipos de cadenas para facilitar su trabajo. Cuando asignamos una cadena a una variable, JS crea un objeto de tipo String; Esto nos permite hacer manipulaciones.

Ejemplos

var carname="Volvo XC60";

var carname='Volvo XC60';

Cada carácter de cadena se puede acceder por su valor de ubicación (índice):

var character=carname[7];

Las citas se pueden colocar dentro de la cadena:

Ejemplo

var answer="It's alright";

var answer="He is called 'Johnny'";

var answer='He is called "Johnny"';

O pueden colocarse entre comillas dentro de la cadena \ usando el carácter sombra:

Ejemplo

var answer='It\'s alright';

var answer="He is called \"Johnny\"";

String Length

• length.El valor numérico que indica la longitud de una cadena de caracteres

Adibidea

var txt="Hello World!";

document.write(txt.length);

var txt="ABCDEFGHIJKLMNOPQRSTUVWXYZ";

document.write(txt.length);

Encuentra la ubicación de una cadena dentro de otra

Ejemplo

var str="Hello world, welcome to the universe.";

var n=str.indexOf("welcome");

Si no fuera un texto de búsqueda, devolvería el valor -1.

La existencia de un contenido

match() metodo

Ejemplo

var str="Hello world!";

document.write(str.match("world") + "<br>");

document.write(str.match("World") + "<br>");

document.write(str.match("world!"));

Cambiar o reemplazar el contenido

replace() El método reemplaza una cadena por otra.

Ejemplo

str="Please visit Microsoft!"

var n=str.replace("Microsoft","W3Schools");

Mayúsculas y minúsculas

toUpperCase() / toLowerCase():

Ejemplo

var txt="Hello World!"; // String

var txt1=txt.toUpperCase(); // txt1 is txt converted to upper

var txt2=txt.toLowerCase(); // txt2 is txt converted to lower

String se convierte en Arrayan

split():

Ejemplo

txt="a,b,c,d,e" // String

txt.split(","); // Split on commas

txt.split(" "); // Split on spaces

txt.split("|"); // Split on pipe

Pruebalo tu»

Caracteres especiales

Barra invertida (\) Aprueba apóstrofes, nuevas líneas, comillas y otros caracteres especiales.

String mal utilizado:

var txt="We are the so-called "Vikings" from the north.";

document.write(txt);

Bien utilizado:

var txt="We are the so-called \"Vikings\" from the north.";

document.write(txt);

Otros caracteres especiales:

JavaScript Strings

A JavaScript string simply stores a series of characters like "John Doe".

A string can be any text inside quotes. You can use single or double quotes:

Example

var carname = "Volvo XC60";

var carname = 'Volvo XC60';

Try it yourself »

You can use quotes inside a string, as long as they don't match the quotes surrounding the string:

Example

var answer = "It's alright";

var answer = "He is called 'Johnny'";

var answer = 'He is called "Johnny"';

Try it yourself »

String Length

The length of a string is found in the built in property length:

Example

var txt = "ABCDEFGHIJKLMNOPQRSTUVWXYZ";

var sln = txt.length;

Try it Yourself »

Special Characters

Because strings must be written within quotes, JavaScript will misunderstand this string:

var y = "We are the so-called "Vikings" from the north."

The string will be chopped to "We are the so-called ".

The solution to avoid this problem, is to use the \ escape character.

The backslash escape character turns special characters into string characters:

Example

var x = 'It\'s alright';

var y = "We are the so-called \"Vikings\" from the north."

Try it yourself »

The escape character (\) can also be used to insert other special characters in a string.

This is the lists of special characters that can be added to a text string with the backslash sign:

Breaking Long Code Lines

For best readability, programmers often like to avoid code lines longer than 80 characters.

If a JavaScript statement does not fit on one line, the best place to break it, is after an operator:

Example

document.getElementById("demo").innerHTML =

"Hello Dolly.";

Try it Yourself »

You can also break up a code line within a text string with a single backslash:

Example

document.getElementById("demo").innerHTML = "Hello \

Dolly!";

Try it Yourself »

However, you cannot break up a code line with a backslash:

Example

document.getElementById("demo").innerHTML = \

"Hello Dolly!";

Try it Yourself »

Strings Can be Objects

Normally, JavaScript strings are primitive values, created from literals: var firstName = "John"

But strings can also be defined as objects with the keyword new: var firstName = new String("John")

Example

var x = "John";

var y = new String("John");

// type of x will return String

// type of y will return Object

Try it yourself »

Example

var x = "John";

var y = new String("John");

// (x === y) is now false because x is a string and y is an object.

Try it yourself »

String Properties and Methods

Primitive values, like "John Doe", cannot have properties or methods (because they are not objects).

But with JavaScript, methods and properties are also available to primitive values, because JavaScript treats primitive values as objects when executing methods and properties.

String methods are covered in next chapter.

String Properties

String Methods

Finding a String in a String

The indexOf() method returns the index of (the position of) the first occurrence of a specified text in a string:

Example

var str = "Please locate where 'locate' occurs!";

var pos = str.indexOf("locate");

Try it Yourself »

The lastIndexOf() method returns the index of the last occurrence of a specified text in a string:

Example

var str = "Please locate where 'locate' occurs!";

var pos = str.lastIndexOf("locate");

Try it Yourself »

Both the indexOf(), and the lastIndexOf() methods return -1 if the text is not found.

Both methods accept a second parameter as the starting position for the search.

Searching for a String in a String

The search() method searches a string for a specified value and returns the position of the match:

Example

var str = "Please locate where 'locate' occurs!";

var pos = str.search("locate");

Try it Yourself »

The two methods, indexOf() and search(), are equal.

They accept the same arguments (parameters), and they return the same value.

The two methods are equal, but the search() method can take much more powerful search values.

You will learn more about powerful search values in the chapter about regular expressions.

Extracting String Parts

There are 3 methods for extracting a part of a string:

• slice(start, end)
• substring(start, end)
• substr(start, length)

The slice() Method

slice() extracts a part of a string and returns the extracted part in a new string.

The method takes 2 parameters: the starting index (position), and the ending index (position).

This example slices out a portion of a string from position 7 to position 13:

Example

var str = "Apple, Banana, Kiwi";

var res = str.slice(7,13);

The result of res will be:

Banana

Try it yourself »

If a parameter is negative, the position is counted from the end of the string.

This example slices out a portion of a string from position -12 to position -6:

Example

var str = "Apple, Banana, Kiwi";

var res = str.slice(-12,-6);

The result of res will be:

Banana

Try it yourself »

If you omit the second parameter, the method will slice out the rest of the string:

Example

var res = str.slice(7);

Try it yourself »

or, counting from the end:

Example

var res = str.slice(-12);

Try it yourself »

The substring() Method

substring() is similar to slice().

The difference is that substring() cannot accept negative indexes.

Example

var str = "Apple, Banana, Kiwi";

var res = str.substring(7,13);

The result of res will be:

Banana

Try it yourself »

If you omit the second parameter, substring() will slice out the rest of the string.

The substr() Method

substr() is similar to slice().

The difference is that the second parameter specifies the length of the extracted part.

Example

var str = "Apple, Banana, Kiwi";

var res = str.substr(7,6);

The result of res will be:

Banana

Try it yourself »

If the first parameter is negative, the position counts from the end of the string.

The second parameter can not be negative, because it defines the length.

If you omit the second parameter, substr() will slice out the rest of the string.

Replacing String Content

The replace() method replaces a specified value with another value in a string:

Example

str = "Please visit Microsoft!";

var n = str.replace("Microsoft","W3Schools");

Try it Yourself »

The replace() method can also take a regular expression as the search value.

Converting to Upper and Lower Case

A string is converted to upper case with toUpperCase():

Example

var text1 = "Hello World!"; // String

var text2 = text1.toUpperCase(); // text2 is text1 converted to upper

Try it Yourself »

A string is converted to lower case with toLowerCase():

Example

var text1 = "Hello World!"; // String

var text2 = text1.toLowerCase(); // text2 is text1 converted to lower

Try it Yourself »

The concat() Method

concat() joins two or more strings:

Example

var text1 = "Hello";

var text2 = "World";

text3 = text1.concat(" ",text2);

Try it Yourself »

The concat() method can be used instead of the plus operator. These two lines do the same:

Example

var text = "Hello" + " " + "World!";

var text = "Hello".concat(" ","World!");

Extracting String Characters

There are 2 safe methods for extracting string characters:

• charAt(position)
• charCodeAt(position)

The charAt() Method

The charAt() method returns the character at a specified index (position) in a string:

Example

var str = "HELLO WORLD";

str.charAt(0); // returns H

Try it Yourself »

The charCodeAt() Method

The charCodeAt() method returns the unicode of the character at a specified index in a string:

Example

var str = "HELLO WORLD";

str.charCodeAt(0); // returns 72

Try it Yourself »

Accessing a String as an Array is Unsafe

You might have seen code like this, accessing a string as an array:

var str = "HELLO WORLD";

str[0]; // returns H

This is unsafe and unpredictable:

• It does not work in all browsers (not in IE5, IE6, IE7)
• It makes strings look like arrays (but they are not)
• str[0] = "H" does not give an error (but does not work)

If you want to read a string as an array, convert it to an array first.

Converting a String to an Array

A string can be converted to an array with the split() method:

Example

var txt = "a,b,c,d,e"; // String

txt.split(","); // Split on commas

txt.split(" "); // Split on spaces

txt.split("|"); // Split on pipe

Try it Yourself »

If the separator is omitted, the returned array will contain the whole string in index [0].

If the separator is "", the returned array will be an array of single characters:

Example

var txt = "Hello"; // String

txt.split(""); // Split in characters

Try it Yourself »

Complete String Reference

For a complete reference, go to our Complete JavaScript String Reference.

The reference contains descriptions and examples of all string properties and methods.