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:
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 start position, and the end position (end not included).
This example slices out a portion of a string from position 7 to position 12 (13-1):
Remember: JavaScript counts positions from zero. First position is 0.
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:
If you omit the second parameter, the method will slice out the rest of the string:
or, counting from the end:
The substring() Method
substring() is similar to slice().
The difference is that substring() cannot accept negative indexes.
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
let str = "Apple, Banana, Kiwi";
str.substr(7, 6) // Returns Banana
The result of res will be:
Banana
If you omit the second parameter, substr() will slice out the rest of the
string.
If the first parameter is negative, the position counts from the end of the string.
Replacing String Content
The replace() method replaces a specified value with another
value in a string:
Example
let text = "Please visit Microsoft!";
let newText = text.replace("Microsoft", "W3Schools");
Try it Yourself »
The replace() method does not change the string it is called on. It returns a new string.
By default, the replace() method replaces only the first match:
Example
let text = "Please visit Microsoft and Microsoft!";
let newText = text.replace("Microsoft", "W3Schools");
By default, the replace() method is case sensitive. Writing MICROSOFT (with
upper-case) will not work:
Example
let text = "Please visit Microsoft!";
let newText = text.replace("MICROSOFT", "W3Schools");
To replace case insensitive, use a regular expression with an /i flag (insensitive):
Example
let text = "Please visit Microsoft!";
let newText = text.replace(/MICROSOFT/i, "W3Schools");
Note that regular expressions are written without quotes.
To replace all matches, use a regular expression with a /g flag (global match):
Example
let text = "Please visit Microsoft and Microsoft!";
let newText = text.replace(/Microsoft/g, "W3Schools");
You will learn a lot more about regular expressions in the chapter JavaScript Regular Expressions.
Converting to Upper and Lower Case
A string is converted to upper case with toUpperCase():
Example
let text1 = "Hello World!"; // String
let text2 = text1.toUpperCase(); // text2 is text1 converted to upper
Try it Yourself »
A string is converted to lower case with toLowerCase():
Example
let text1 = "Hello World!"; // String
let text2 = text1.toLowerCase(); // text2 is text1
converted to lower
Try it Yourself »
The concat() Method
concat() joins two or more strings:
Example
let text1 = "Hello";
let text2 = "World";
let 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
text = "Hello" + " " + "World!";
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.
String.trim()
The trim() method removes whitespace from both sides of a string:
JavaScript String Padding
ECMAScript 2017 added two String methods: padStart
and padEnd to support padding at the beginning and at the end of a string.
String Padding is not supported in Internet Explorer.
Firefox and Safari were the first browsers with support for JavaScript string padding:
| Chrome 57 | Edge 15 | Firefox 48 | Safari 10 | Opera 44 |
| Mar 2017 | Apr 2017 | Aug 2016 | Sep 2016 | Mar 2017 |
Extracting String Characters
There are 3 methods for extracting string characters:
charAt(position)charCodeAt(position)- Property access [ ]
The charAt() Method
The charAt() method returns the character at a specified
index (position) in a string:
The charCodeAt() Method
The charCodeAt() method returns the unicode of the character
at a specified index in a string:
The method returns a UTF-16 code (an integer between 0 and 65535).
Property Access
ECMAScript 5 (2009) allows property access [ ] on strings:
Property access might be a little unpredictable:
- It makes strings look like arrays (but they are not)
- If no character is found, [ ] returns undefined, while charAt() returns an empty string.
- It is read only. str[0] = "A" gives no error (but does not work!)
Example
let text = "HELLO WORLD";
text[0] = "A"
// Gives no error, but does not work
text[0] // returns H
Try it Yourself »
If you want to work with a string as an array, you can convert it to an array.
Converting a String to an Array
A string can be converted to an array with the split() method:
Example
text.split(",") // Split on commas
text.split(" ") // Split on spaces
text.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:
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.
