Best practices for programming secure code with TypeScript

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After its introduction, TypeScript elicited various responses from the JavaScript community. Some have endorsed it, while others have rejected it vehemently. Regardless of the reactions, TypeScript has offered several improvements that make it helpful in developing large applications. It also provides certain security advantages while not being without its flaws.

Learn more about TypeScript, the differences between JavaScript and TypeScript programming, and some good security practices below!

What is TypeScript?

TypeScript (TS) is an open-source, object-oriented programming language developed by Microsoft in 2012. It was developed due to JavaScript (JS) becoming too complex when developing large applications. It can be used for both client-side and server-side development.

TypeScript is a strict superset of JavaScript, meaning existing JS applications are also valid TS applications. JS libraries are compatible with TS and can be incorporated. 

Several of its essential features are optional static typing (thanks to type definition), strict type binding, and type inference. First, type checking is performed at compilation, reducing runtime errors. Type binding means that variables are bound to specific data types, and type inference denotes the ability of the compiler to find types alone, without additional input by developers.

Besides its more advanced type system, TS introduces object-oriented features to ECMAScript 6 like interfaces, enumerated types (enums), generics, tuples, async/await, and more. It also includes previous ECMAScript 2015 features such as classes, modules, optional and default parameters, etc. 

However, despite its advantages, TypeScript is not natively supported by browsers and is hence not understood by browser engines. To be run in a browser, it is transpiled (i.e., translated) into JavaScript by the default TypeScript Checker (tsc) or some other transpiler. 

All of the above makes TypeScript very useful when developing larger applications. While it may increase compilation time, require more code, and take time to learn, it offers greater application security and robustness. It allows developers to spot security issues and refactor the code throughout, building a more solid and error-proof application.

TypeScript vs. JavaScript: what are the differences?

Both TypeScript and JavaScript have their advantages and disadvantages. Here is a comparison between the two languages, their main features and aspects, and what each programming language is or isn’t suitable for.

DefinitionA superset of JavaScript that was developed to resolve code complexity issues for large projects. It is a dependent language that compiles to JavaScript.An independent scripting language that is used to create dynamic and robust web page content. 
ParadigmPrototype-based object-oriented scripting language. Provides support for a class-based approach.Prototype-based object-oriented scripting language.
Typing and annotationStrong typing, optional static and dynamic typing.Weakly typed, dynamic typing.
CompilationCode is transpiled into JavaScript and compiled. Cannot be executed directly by browser engines.No compilation. JS is an interpreted language and is directly executed by browsers. 
LibrariesCan use all JS libraries and code.Uses default JS libraries.
ErrorsCan be found during compilation and fixed.Established during runtime, since no compilation.
StructureMore structured and explicit due to the type system.More flexible due to not being limited by a type system.
FunctionsCan have optional parameters.Cannot have optional parameters.
Data bindingSupports interfaces, modules, and generics.Does not provide support.
PrototypingOffers prototyping.Does not offer prototyping.
ECMAScript supportCompiler can compile into ES3, ES4, ES5, ES6, and ES7 and supports their features.Does not provide support for compiling additional ES3, ES4, ES5, or ES6 features.
Project sizeGood for large, complex projects.Good for small and medium projects.
CommunitySmaller community, still growing.Large community with a lot of support.
Learning curveRequires prior scripting knowledge and takes time to learn.Easier to learn and flexible does not require prior knowledge.

These are the main differences and similarities between the two languages. Depending on the needs of a project and the team’s capabilities, each of them can be right.

What problems does TypeScript solve? 

In particular, TypeScript solves several significant problems regarding large projects.

Greater ability to spot bugs

Typically, bugs are spotted via automated tests and manual checking, and code review with JS. This is fine if a project’s codebase doesn’t include hundreds or thousands of files. Changing the code in one file may impact other files, which, at scale, can introduce many bugs down the road.

TS validating connections between files and spotting bugs early is automated and improved. Many bugs can be sorted out at the compile stage, reducing the time and resources spent on quality assurance and testing. While security checks are not absent from JS, TS is beneficial for higher-level logic errors.

More structure and solidity

Strict typing guarantees that once the variable type is set, it doesn’t change and is limited in the values it can take. This feature provides a vital security guarantee because it prevents the reassignment or comparison of types without explicit declaration. Particular vulnerabilities in the Common Weakness Enumeration (CWE) can only be addressed via strict typing.

This feature is not only crucial for catching bugs and avoiding security vulnerabilities but also because it makes the code self-documenting and more readable. Yes, this may indeed introduce more code in total. However, this code provides greater structure, readability, and predictability, aiding debugging and refactoring.

Increased productivity

TypeScript programming is known for the productivity boost it provides. This is thanks to the varied and rich integrated development environments (IDE) support and various development tools that come with it, such as autocompletion and code navigation.

Along with the automated compiling and documentation, the significantly faster feedback cycle, and the greater structure provided by the language, the developer’s cognitive load is reduced considerably, opening up more bandwidth for creativity and productivity.

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Best practices for cybersecurity in TypeScript

Following are some best practices that increase TypeScript security, help develop more robust and transparent code, and help you make the most out of TS.

  • Use the correct type declaration: annotating types in advance helps reduce runtime errors. Avoid using “any” if you know what type of data the variable will hold, as the TS compiler will treat it as a signal to avoid type checking.
  • Use strict mode: one of the most important features of TS, this helps you avoid making accidental mistakes such as leaving undeclared variables, forgetting to use type annotation, etc.
  • Use primitive types: instead of using non-primitive boxed objects such as Number, String, Boolean, Symbol, or Object, opt for primitive and general types such as number, string, boolean, symbol, and object. The former is rarely used appropriately in JS and could create issues.
  • Use ‘let’ not ‘var’: let is a blocked scope variable declaration that, unlike var, cannot be redeclared or called without declaring it. Moreover, TS will not report errors associated with var
  • Declare constants with const: similar to let, const cannot be redeclared. However, let values can be updated, while const is used to declare constants, and its importance cannot be updated. 
  • Use opaque and utility types: using opaque types helps TS distinguish between types and validate their values (which gets lost with string-typed parameters). Utility types, on the other hand, will make your code more comprehensive and reduce redundant/duplicate types. 
  • Use return type ‘void’ instead of ‘any’ for callbacks: for callbacks whose values will be ignored, use void. This prevents accidentally using the value of a function that is not checked.
  • Use Babel and the whole ecosystem: using Babel instead of the TypeScript Checker makes transpiring much faster. It also enables you to use all the tools available in the Babel ecosystem. 

The above are some good practices you can implement to improve the quality and security of your TypeScript code. For more best practices and tips, see the TypeScript website.


What are the benefits of TypeScript?

TypeScript is an open-source superset of JavaScript which is very useful for large-scale projects with a big codebase. Thanks to its optional static and strong typing, type inference, and type definition, it provides greater application security, structure, and readability of the code. A great number of errors are found already while compiling, reducing bugs at a later time. 

What are the disadvantages of TypeScript?

TypeScript’s typing system can seem excessively difficult. Moreover, TS compilation is inevitable, which adds time to the process. In addition, more learning and prior scripting knowledge are required to work with TS. 

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