I see this line of code in some of the JavaScript Files I work with, at the very top of the file ( first line ), but its not clear to me exactly what this does.
Google wasn't much help on this.
/// <reference path="jquery-1.8.3.js" />
What is the purpose of it?
To add more details, I am using Visual Studio 2015.
This is most likely for Visual Studio's JavaScript intellisense. Mads Kristensen has a nice article you can read to learn more about the history of this and how to use it correctly.
That is a triple-slash directive for the Typescript compiler. Since tsc will happily compile JS as well, this should work in either language and will reference a dependency.
The /// <reference .../> directive shows a dependency (for compiler symbols) without necessarily importing and actually loading the file. That is useful when you have a large library (like React) that exports a lot of interfaces or type symbols, but you don't want to actually include (since they might be vendored at runtime). From the docs:
The /// directive is the most common of this group. It serves as a declaration of dependency between files.
Triple-slash references instruct the compiler to include additional files in the compilation process.
Related
If you were to write your own open source typescript library how would you structure the typescript and the typescript definitions? From what I understand the definition files are really there for the compiler so that when your library gets consumed there is intellisense to help the consumer.
However, how do definition files work internally when developing a library? Would you put all of your types (interfaces, classes, etc) in a {module}.d.ts file and reference the definition file internally so that you don't have to write the types twice (once in the {module}.ts and once in the {module}.d.ts?
In the typescript compiler options what is the point of setting "declaration" to true? To me it doesn't seem helpful to automate the definition file creation if it won't be very helpful (i.e. comments).
If your library has multiple modules would you write a separate definitions for each module and add references between definitions then concatenate them with some automater (i.e. gulp, grunt)?
What is the recommended way to expose your library so that both typescript consumers and javascript consumers can use your library?
How would you write tests in typescript? Would you import the typescript modules in your test files?
When developing your library in typescript you do not use definitions of your own classes. They are 'self contained' and already provide all type information to transpiler/IDE. The definitions are as you have mentioned for external consumers.
The point of setting declaration to true is to get rid of tedious job of collecting type information from typescript classes and pasting it in definition files. As I have said this information is already present in typescript files and can be automatically extracted by transpiler.
Regarding the way of how to organize your definitions and expose them - I am sure there are multiple different ways, one thing for sure - you do not want to write the same class definitions manually in two places. Having said that I can give you a sample of how I expose library project and consume it in another one.
Pay attention to index.ts files there and how the root one is exposed in package.json -> typings field. There you will also find exampls of unit tests for the library via jasmine.
Hope this will give you some information of how to go process with your library development.
I would like to use a javascript function inside a typescript file. How can I reference the javascript file containing that function inside typescript file?
I tried
<reference path="../libs/myjsfile.js" />
this brings an error while building like: Cannot resolve referenced file: ../libs/myjsfile.js
While the two answers above will work for a small or single variable API, the correct answer is to write a type declaration file for your JavaScript file.
The type declaration file for your example would be named myjsfile.d.ts, where the .d.ts suffix is what tells the TypeScript compiler that it's parsing a declaration file. If you use Visual Studio, your declaration file will be recognized by the TypeScript compiler as long as it is somewhere (anywhere) in the project you are working on.
Declaration files store metadata about JavaScript variables, functions and objects so the TypeScript compiler can do its job. If your JavaScript file happens to be a library or framework in common use, DefinitelyTyped is definitely the place to find the definition file you need.
If your JavaScript is your own work or less well known, you'll have to write your own type declaration file. See the section Writing .d.ts files in The TypeScript Handbook.
If the name declaration file sounds intimidating, don't worry - they are far easier to write than programs. Also, remember that you don't need to specify all metadata for your JavaScript file, just the functionality you need.
Let me know if you need any help!
You just have to tell the compiler that the method exists outside typescript:
declare function myJavaScriptFunction(param1: number, param2: JQuery): void;
Be sure that the website loads all files needed, the normal js files and the js files that the typescript compiler generated
You can see the latest version of the TypeScript documenttion in TypeScript
Handbook on GitHub:
Working with Other JavaScript Libraries
Writing Definition Files
Also I am recomending you the tsd utility to search and install TypeScript definition files directly from the community driven DefinitelyTyped repository. This repository contains definition files *.d.ts for the most popular javascript libraries.
this brings an error while building like: Cannot resolve referenced file: ../libs/myjsfile.js
Reference file tags are for TypeScript not JavaScript. You would load JavaScript using a script tag in your page (or something like requirejs).
To use the JavaScript from TypeScript you would declare the API of the javascript you want to use for TypeScript consumption (as AKR pointed out).
In Visual Studio 2012, I created a web application then found the following line in the default _references.js script that came with the project:
/// <reference path="jquery-1.8.2.js" />
What is this reference notation doing? This is confusing - isn't this just a comment, which shouldn't do anything? As I understand, a double slash (//) comments out a line in JavaScript. Is there anything special about triple-slash comments?
see this article
http://msdn.microsoft.com/en-us/library/vstudio/bb385682.aspx
and find Reference Directives
A reference directive enables Visual Studio to establish a relationship between the script you are currently editing and other scripts. The reference directive lets you include a script file in the scripting context of the current script file. This enables IntelliSense to reference externally defined functions, types, and fields as you code.
It's a Triple Slash Directive and has many uses.
See this article
https://www.typescriptlang.org/docs/handbook/triple-slash-directives.html
... Triple-slash references instruct the compiler to include additional files in the compilation process....
Very useful in linking typings definitions... for example, the mysql.d.ts typings has the following reference to the node.js typings...
///<reference path='../node/node.d.ts' />
Suddenly VS2012 stopped building javascript files from my typescript files. Options look ok. Also tried do uninstall web essentials without success.
Only when I completely restart VS the JS files are generated.
Edit1: seems that breeze.d.ts makes the problems. I am getting the error as soon as i reference it:
/typings/breeze/breeze.d.ts(213,5): error TS1038: 'declare' modifier not allowed for code already in an ambient context.
Edit2: also seems that typescript has still (v0.9) many bugs concerning references and paths.
For example you can't use spaces as you want
right:
/// <reference path="typings/jquery/jquery.d.ts" />
wrong:
/// <reference path= "typings/jquery/jquery.d.ts" />
The error you're receiving is caused by the fact the declare statement is used in the Breeze definition file, which isn't allowed. Definition files do not require the use of the declarestatement to declare variables, modules or interfaces.
I've encountered similar behaviour where an error in one of my referred definition files caused Visual Studio to stop compiling TypeScript without throwing an error. I'm not sure if this is an error on the part of Web Essentials or the TypeScript compiler.
I was able to get over this error by deleting a semicolon:
declare module 'asdf' {
};
^ deleted the above semicolon
Is it only possible to get intellisense in TypeScript files by referencing .ts files with own coded interfaces?
Is there a solution for existing JavaScript libraries?
You are able to get IntelliSense for other TypeScript files by using an external script reference directive at the top of your script:
///<reference path="someOtherScript.ts" />
As a side note, the TypeScript IntelliSense reference directive doesn't support the tilde operator like the JavaScript reference directive does. For example, if your script is located in "~/Scripts/foo/", in JavaScript you can reference:
///<reference path="~/Scripts/otherScriptFile.js" />
whereas in TypeScript you have to reference relative to the current file:
///<reference path="../otherScriptFile.ts" />
More info about this can be found in section 11.1.1 Source Files Dependencies of the TypeScript Spec.
With regard to JavaScript IntelliSense in a TypeScript file, it currently appears to be not possible to get JavaScript reference IntelliSense.
As others before me have pointed out, you need the definition files.
The DefinitelyTyped GitHub repository provides an excellent (and growing) list of definition files for a lot of popular libraries.
You'll get intellisense support for every JS code (quality may vary), however the typescript specific stuff is only available when using apropriate definition files (*.d.ts).
You can find additional definition files in the source repository (> typings, currently only jQuery and WinJS/RT) http://typescript.codeplex.com/SourceControl/BrowseLatest