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TSVG: Turing-complete SVG preprocessor, using JSX and JavaScript.

Turing-complete SVG preprocessor

TSVG is a Turing-complete SVG preprocessor, using JSX and JavaScript. Much like LessJS is a superset of CSS with very useful abstractions and error- and time-saving features, TSVG is a superset of SVG.

Features and Benefits

The "T" stands for:

  • Turing-complete: use a real programming language whose syntax you know (JSX is easy to learn -- you already know JavaScript and XML). TSVG does not use string interpolation, but builds real light-weight trees with attributes and children at runtime, then serialzies to text strings which can be exported to .svg. TSVG is completely declarative and by embedding modern JS (ES6) into SVG you get a concise, expressive functional language. Use helper tags like For and If, and helpers like @translate(x,y) to keep things concise.
  • TextPath: use SVG fonts to render baked-out path outlines into your SVG, which will look the same on all devices -- the .svg file will have no external file dependencies. (The JS code that renders SVG will include a JSON-ified version of the SVG font(s). You can also whitelist a specific set of glyphs, reducing the output file size substantially.) <TextPath> mimics much of the API for SVG's <text> tag, including attributes and layout arithmetic, down to kerning and letter spacing.
  • Templates: a compact way to 'write' JS template code, with variables that can be reassigned later, then call render() and get a new SVG at runtime -- in the browser (ES5) or in Node.js. Your code has no dependencies since the lightweight TSVG helper library is added to the generated JS. You can also combine multiple templates into one compiled file, resulting in only one copy of the TSVG helper code and fonts. Combined with TextPath, this is a powerful way to add professional, dynamic typography to the SVG parts of your applications.


TSVG is built with Node.js. Install with:

npm install -g tsvg

to access the command-line tool from anywhere on your system, or for local use in a given project,

npm install --save tsvg

and look for node_modules/tsvg/bin/tsvg.


TSVG is (nearly) a superset of SVG (including allowing attributes like xmlns:xlink="whatever", a hack to work around limitations in JSX). This means (with a few caveats, read below) that you can rename .svg files to .tsvg and compile them with the tsvg command-line tool and get back essentially the same .svg file.

TSVG augments SVG with JavaScript code via JSX. (TSVG provides its own React.createElement implementation, which creates nested FakeElements, which have a .render() method that can be used to get SVG back out of the in-memory trees. This React class and other helpers are not added to the global scope but everything is hygenic.) This is not a hacked together, string-concatenation-based approach to creating SVG, but a grammatical, structural, purely-functional, tree-based approach.

When you create a TSVG file, you are creating a pure JavaScript function that takes an (optional) object with key value pairs and, by calling .render(), returns a string of SVG. This works in the browser or on the server.

Example of Some Advanced Results You Can Achieve with TSVG

  • Ebookshelf
    A Virtual Bookshelf view of the books available at Standard Ebooks as a Virtual Bookshelf, a graphic design project by Jared Updike. The spine of each book is an SVG image, rendered by JS code output by TSVG (each book's title, author, etc. is passed in as arguments to the render function).

Basic "preprocessor" approach

TSVG embeds the expressive parts of JS, allowing anything from lightweight use to heavy use of JavaScript. For example

<svg version="1.1" xmlns=""
    xmlns:xlink="" x="0" y="0" width="800" height="800"
    viewBox="0 0 800 800" preserveAspectRatio="xMidYMid none">
  <line x1="0" y1="200" x2="780" y2="200"/>
  <line x1="0" y1="400" x2="780" y2="400"/>
  <line x1="0" y1="600" x2="780" y2="600"/>

could become

<svg version="1.1" xmlns="" 
    xmlns:xlink="" x="0" y="0" width="800" height="800"
    viewBox="0 0 800 800" preserveAspectRatio="xMidYMid none">
  <line x1="0" y1={200*1} x2="780" y2={200*1} />
  <line x1="0" y1={200*2} x2="780" y2={200*2} />
  <line x1="0" y1={200*3} x2="780" y2={200*3} />

JavaScript code is introduced as the right-hand side of an equals sign on an attribute with {code} instead of "str". (When the render code walks the tree, this double/number gets converted to a string.) JavaScript code is introduced as a child with

<rect x="" ... />
{@callMyFunction(arg1, arg2, arg3)}
<rect x="" ... />

But where do such @callMyFunction methods live?

@abc =>

Stealing an idea from Coffeescript, we use @abc as syntax sugar for TSVG's built-in library helper methods (translate, lines, makeStyle, etc.) are added to the this object context when your generated JavaScript code is called, before render is called. So

<rect x="" ... />
<rect x="" ... />

can call the built-in helper lines(..)

Define your own "global" (const) parameters and helpers

@abc = "my variable";

Using @abc = arbitrary("JavaScript", "goes", here"); you can make your own 'global' constants and helpers.

<svg version="1.1" xmlns="" 
    xmlns:xlink="" x="0" y="0" width="800" height="800"
    viewBox="0 0 800 800" preserveAspectRatio="xMidYMid none">
  @verticalGap = 200;
  <line x1="0" y1={@verticalGap*1} x2="780" y2={@verticalGap*1} />
  <line x1="0" y1={@verticalGap*2} x2="780" y2={@verticalGap*2} />
  <line x1="0" y1={@verticalGap*3} x2="780" y2={@verticalGap*3} />

To make a helper, use arrow syntax on the right hand side:

<svg version="1.1" xmlns="" 
    xmlns:xlink="" x="0" y="0" width="800" height="800"
    viewBox="0 0 800 800" preserveAspectRatio="xMidYMid none">
  @verticalGap = 800;
  @lineMaker = yIndex => <line x1="0" y1={@verticalGap * yIndex} x2="780" y2={@verticalGap * yIndex} />;

The semicolon used to declare a constant is required, but do not put semicolons in calls to @lineMaker(3) because it is an expression, not a statement. Notice also that the yIndex variable is local to that function, so is not prefixed with @. Notice also that <tag attr1="whatever" attr2="wherever"/> is valid JavaScript code that can be used anywhere a tag can be used.


Continuing the running example, you can use the For component (built-in tag) as follows:

<svg version="1.1" xmlns="" 
    xmlns:xlink="" x="0" y="0" width="800" height="800"
    viewBox="0 0 800 800" preserveAspectRatio="xMidYMid none">
  @verticalGap = 800;
  @lineMaker = yIndex => <line x1="0" y1={@verticalGap * yIndex} x2="780" y2={@verticalGap * yIndex} />;
  <For from="1" upTo="3">
    {i => @lineMaker(i)}
    {i => @rectMaker(i)}

Each function is invoked with the loop variable (which has no name besides the one you give it in the arrow function) and the results inserted as children. You can also nest For loops.

Note that the upTo argument is inclusive of the value. Also note that these strings are converted to numbers before the loop starts, and you can put <For from={0} upTo={@x-1}> or any other JavaScript code, as you would expect.

(You cannot mutate 'global' @parameters because they are pulled out long before the code is run. You can define @parameters more than once, but the last definition wins. Recursion is unsupported and untested.)


Your generated JS code can be called with

window.TSVG.Templates['my-file-name']({'abc': 123, 'efg': 456}).render();

in order to pass parameters to your TSVG code. (It is recommended to put in default values for @abc and @efg so you can generate SVG directly without changing the specific parameters externally, making development and testing easier.)

Template / parameters Caveat

Your parameters can depend on each other, but the order of the generated code is:

this['helper'] = ...;   // from TSVG library helpers
this['abc'] = ...;      // from your TSVG file
this['abc'] = ...       // from the call, as above

This allows the call to the JS code to override the TSVG file, but in order for @parameter code to depend on each other, wrap it in an arrow:

@height = 800;
@quarter = () => +(@height) / 4;
<line x={@quarter()} ... >

This is a limitation of JavaScript not being a lazy, purely functional language.

In addition, in order to handle string arguments as numbers, convert them to doubles/numbers as in:


TextPath, Font

Here is a simple example of the drop-in SVG <text> replacement tag, TextPath:

<svg version="1.1" xmlns="" xmlns:xlink="" x="0" y="0" width="600" height="180" viewBox="0 0 600 180">
  <Font path='./svg-fonts/firasanscondensed-bold.svg'/>
    x="300" y="120"
    style="fill: orange"
    >Hello World</TextPath>
    x="300" y="120"
    font-family="Fira Sans Condensed"
    fill="transparent" stroke="black" stroke-width="1px" 
    >Hello World</text>

If the Font path attribute starts with a . or .., the path of the current .tsvg file is prepended. If you install the included .otf file on your system, then you can see how the two compare by loading the output of npm test, textpath.svg, in your browser.

You can also whitelist characters, in order to keep the output .JS files small:

<Font white-list-chars='abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ,.; ' path='./svg-fonts/firasanscondensed-bold.svg'/>

Notice that you cannot put a newline inside this tag between white-list-chars and path and you must put white-list-chars first (if present) and you must match the single or double quote marks, due to limitations in the Font Regex-based preprocessor.

The Font tag will parse the .svg font file specified by path, as XML, and convert it to a normalized .JSON representation. TSVG will cache this as font-abcdef1234567890.json to speed up subsequent runs of tsvg. (The hash includes the contents of the file and the white listed characters, if any, so should be stable.)

The TextPath tag uses (some of) the same attributes as the SVG text tag, including those in the example above, as well as letter-spacing. (Ligatures like fi ff are supported, but not when letter-spacing is used. This matches the text tag) The TextPath-specific attribute font-id is mandatory (to know which font to use) but could later use the same system as the <text> tag, with family and weight.

In order to convert .otf and .ttf fonts to .svg fonts, just search online for converters, or use FontForge at home. (FF's UI is terrible on the Mac, so I use it from the command-line. YMMV.) Remember that professional fonts have license restrictions, so good luck navigating that.


(!) do not put newlines inside of attributes, for example <path d="whatever NEWLINE whatever"/> because it will not parse correclty. This is a limitation of JSX.

(!) do not include <!DOCTYPE> or <?xml ...> -- just remove them completely. The generated JSX code looks like: TSVG.Templates['my-file-name'] = <svg ...>...</svg> before it is compiled to vanilla JS, so this must be exactly one element (does not have to be svg, could be path or whatever, must be a single element)

(!) @xyz = rhs; -- right hand side cannot have ; characters, even inside a string. Use @makeStyle({a: b, c: d}) instead.

(!) Quirk of parsing Font tags: only these four forms work!

<Font path="" />
<Font white-list-chars="" path="" />  (not path followed by white-list-chars)
<Font path='' />
<Font white-list-chars='' path='' />  (don't mix single and double quotes)

(!) another quirk: in order to white-list the space character (ASCII = 32, you know the one), you must put it at the end of the white-list string

(!) if you are whitelisting the same font and using it in multiple files, which get compiled into a single .js file with embedded fonts (using --ouput or -o), make sure the whitelist characters are the same in each TSVG file for that font, so that the order of compiling the input .tsvg files will not matter and you won't be missing glyphs (characters) from that font

Helper Methods

@translate(x: string, y: string)
@rotate(x: string, ox=0, oy=0)
@line(x1: string, y1: string, x2: string, y2: string, opts: { [k: string]: any; })
@with(obj1: any, key: string, rhs: any)
@closedPolyPath(opts: { [k: string]: any; }, d: string[])
@lines(opts: { [k: string]: any; }, pointPairs: Array<[any, any, any, any]>)
@range(a: number, b: number = undefined)
@flatten(array: any)
@textWidthHelper(fontId: string, fontSize: number, style: any, textStr: string): number

Command-line arguments


  $ tsvg input.tsvg                        1. Convert input.tsvg to input.svg.                          
  $ tsvg input2.tsvg -a width:100          2. Convert input2.tsvg to input2.svg; pass argument "@width" 
                                           as "100".                                                    
  $ tsvg *.tsvg -o tsvg-all.js -g window   3. Convert multiple .tsvg files to one .js file (can call    
                                           "args"}).render() to generate SVG string).                   


  -h, --help                print this usage help and exit                                               
  -k, --keep                do not delete, .js and .tsx temp files (.tsvg -> .tsx -> .js ->      
                            .svg); overwrite them if they exist (default is to delete upon success, and  
                            to bail if those files exist -- so as not to delete anything important)      
  -f, --force               Always overwrite, .js and .tsx temp files (.tsvg -> .tsx -> .js ->   
                            .svg); they do not contain anything important                                
  -s, --src file.tsvg ...   (default if no flag specified) the input .tsvg files to process; by default  
                            x.tsvg will output x.svg (see --output below)                                
  -a, --args k:v ...        one or more k:v pairs passed to the template, where @k takes the value v,    
                            e.g.  tsvg --arg k:v  results in {k: 'v'}  passed to template                
  -q, --quiet               produce no .svg ouput; generated .js code does not call                      
                            console.log(TSVG.Templates[<mine>]().render());  as is the default, for      
                            generating .svg files                                                        
  -o, --output to/file.js   combine all .js code from all .tsvg src files into a single .js file,        
                            instead of generating .svg file(s); turns on --quiet as well                 
  -g, --global string       define the global object to attach templates code to; for example  --global  
                            window generates code   window['TSVG'] = TSVG;  this turns on --quiet as     
  -d, --dev                 a special flag for development, to force TypeScript files to be recompiled   
                            each time tsvg binary runs

Future Work

  • --jshelper ClassName (-j flag) to allow one to specify external JS (ES6) code, a class to pull methods out of and add to generated code and 'this' object.

  • More interesting, better examples -- as a sort of test suite

  • Gallery of awesome examples

  • <If> tag would be easy and useful -- include or not include based on

    <If cond={JavaScript code here}> ...

  • TextPath could use font-family and weight to find the right font-id instead of the current method, which is more confusing since you have to check the .svg font file for the right font-id string.

  • TextPath could match more and more of the attributes in the W3 spec, especially the alignment and letter spacing properties.

  • TextPath could maybe have some way to use alternate glyphs (lower v. upper case numbers, etc.)

  • replace TypeScript with custom Bablyon parser to fix all the parsing issues (esp. ; in right-hand side of @abc = rhs; and quoted @ symbols getting turned into this.)

  • improve error reporting significantly, esp. by making sure new babelscript-based TSVG system would correctly carry source maps through from .tsvg to .js so figuring out where a problem happened would be easier

Shout Out

  • TSVG's approach to parsing and rendering SVG fonts (especially creating transformed path objects) is based on a partial port of EasySVG.php, although TSVG's TextPath supports the hkern attribute and is more accurate.