Dart Libraries

In Dart, the library is the collection of the routine or set of programming instructions. Dart consists of many sets of built-in libraries that are beneficial to hold routines (functions, set of classes, etc.), and regularly used. A Dart library contains constants, functions, properties, exceptions, and typedefs, and set of classes.

Importing a library

  • Importing makes the components in a library available to the caller code.

  • The import keyword is used to achieve the same. A dart file can have multiple import statements.

  • Built in Dart library URIs use the dart: scheme to refer to a library.

  • Other libraries can use a file system path or the package: scheme to specify its URI.

  • Libraries provided by a package manager such as the pub tool uses the package: scheme.

The syntax for importing a library in Dart is given below

import 'URI'

Consider the following code snippet

import 'dart:io' 
import 'package:lib1/libfile.dart' 

If you want to use only part of a library, you can selectively import the library. The syntax for the same is given below

import 'package: lib1/lib1.dart' show foo, bar;  
// Import only foo and bar. 

import 'package: mylib/mylib.dart' hide foo;  
// Import all names except foo

We are describing some commonly used libraries below.

dart:ioThis library consists of File, HTTP, socket, and other I/O support for server applications. This library is not suitable for browser-based applications. We don’t need to import explicitly because it is imported by default.
Dart:coreThis library consists of Collection, built-in types, and other core functionality for each dart program. It is imported by default.
Dart: mathThis library consists of the rich mathematical functions, constant, and random number generator.
Dart: convertIt is used to Encoders and decoders for converting the different data representations such as JSON and UTF
Dart: typed_dataIt represents the lists that store the fixed-sized data efficiently (for example - unsigned 8-byte integer).

Importing and using a Library


import 'dart:math';   // Importing built-in library  
void main() {   
   print("Square root of 36 is: ${sqrt(36)}");   


Square root of 36 is: 6.0


  • Dart provides the facility to encapsulate or restrict access the content of the dart library.

  • It can be done by using the _(underscore), followed by the identifier.

  • The _(underscore) symbol makes the library’s content completely private.



Creating Custom Libraries (User-defined Library)

We can also use our own code as a library and import it when needed. This type of library is called a custom library. Below are the steps to create a custom library.

Step 1 - Declaring a Library

The library statement is used to create a library explicitly. The syntax is given below.


library library_name    
// library contents go here   

Step 2 - Connecting a Library

We can connect a library in two ways.

Within the same directory

import 'library_name'  

From a different directory

import 'dir/library_name'  

Library Prefix

If you import two libraries with conflicting identifiers, then you can specify a prefix for one or both libraries. Use the ‘as’ keyword for specifying the prefix.


import 'library_uri' as prefix

Name Alias of Library

  • Dart allows us to import multiple libraries into the current working file, but if we create the same function name within the different libraries, it will create conflict while accessing these functions.

  • The Dart compiler might be confused to identify the particular function in different library.

  • To overcome this scenario, Dart provides the as keyword for specifying the prefix.


import 'library_uri' as prefix