JavaScript String Methods
String methods help you to work with strings.
String Methods and Properties
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 Length
The length property returns the length of a string:
Example
var txt =
"ABCDEFGHIJKLMNOPQRSTUVWXYZ";
var sln = txt.length;
»
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");
»
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");
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Both the indexOf(), and the lastIndexOf() methods return -1
if the text is not found.
JavaScript counts positions from zero.
0 is the first position in a string, 1 is the second, 2 is
the third ...
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");
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Did You Notice?
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
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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
»
If you omit the second parameter, the method will slice out
the rest of the string:
Example
var res = str.slice(7);
»
or, counting from the end:
Example
var res = str.slice(-12);
»
Negative positions do not work in Internet Explorer 8 and
earlier.
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
»
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
»
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",
"Omegas");
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The replace() method can also take a regular expression as
the search value.
By default, the replace() function replaces only the first
match. To replace all matches, use a regular expression with a g flag (for
global match):
Example
str = "Please visit Microsoft!";
var n = str.replace(/Microsoft/g,
"Omegas");
»
The replace() method does not change the string it is called
on. It returns a new string.
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
»
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
»
The concat() Method
concat() joins two or more strings:
Example
var text1 = "Hello";
var text2 = "World";
text3 = text1.concat(" ", text2);
»
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!");
All string methods return a new string. They don't modify the
original string.
Formally said: Strings are immutable: Strings cannot be
changed, only replaced.
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
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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
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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
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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
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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.
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