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A library for writing type-safe HTML in Golang
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README.md

htmlgo

A library for writing type-safe HTML in Go

This blog post provides a short introduction.

Why?

As much as I like the simplicity and the contextual escaping of html/template, it doesn't provide much type safety. Pipelines (e.g. {{.DoesNotExist.Value}}) can produce errors at runtime, which should be caught during compilation. Using nested templates with html/template can become hard to maintain, as a template user has to inspect the pipelines within a templates to infer the data format to be passed into the template. As a bonus, using Go functions to produce HTML elements prevents malformed HTML.

This library is inspired by Haskell's blaze-html.

Status

  • Support for all HTML5 tags and attributes
  • Secure, contextual escaping (based on html/template)
  • Not optimised for performance, expect it to be significantly slower than html/template

API

Tags

Functions for all HTML tags are part of the top-level package htmlgo. The function signatures are Tagname(attrs []attributes.Attribute, children ...HTML) HTML To omit the first argument, i.e. to create an element without attributes, there are functions with an underscore suffix Tagname_(children ...HTML) HTML to reduce verbosity.

Attributes

Functions to create attributes are located in the package htmlgo/attributes. Use Attr(attrs ...attributes.Attribute) from htmlgo as a less verbose way to create a slice of attributes. The function signatures are Attributename(data interface{}, templates ...string) Attribute. The data will be placed into the given templates using html/template and, therefore, follows the same syntax. Note, as templates is a variadic argument, it can be omitted entirely, in which case a {{.}} template is used. Data provided as data will be escaped, whereas the templates itself can be used to provide values which shall not be escaped. Again, there are convenience functions with an underscore suffix to omit the first argument, which is data in this case Attributename_(templates ...string) Attribute. Use the underscore-suffixed attribute functions wisely, as they will not escape their arguments. A good rule of thumb is that you should never pass a variable into the suffixed functions, only string literals.

The dataset attributes data-* can be added using Dataset(key, value string).

Example

package main

import (
    "fmt"

    . "github.com/julvo/htmlgo"
    a "github.com/julvo/htmlgo/attributes"
)

func main() {
    var numberDivs HTML
    for i := 0; i < 3; i++ {
        numberDivs += Div(Attr(a.Style_("font-family:monospace;")),
                          Text(i))
    }

    page :=
        Html5_(
            Head_(),
            Body_(
                H1_(Text("Welcome <script>")),
                numberDivs,
                Div(Attr(a.Dataset("hello", "htmlgo"))),
                Script_(JavaScript("alert('This is escaped');")),
                Script_(JavaScript("This is escaped", "alert({{.}});"))))

    fmt.Println(page)
}

will output:

<!DOCTYPE HTML>
<html>
  <head>
  </head>
  <body>
    <h1>
      Welcome &lt;script&gt;
    </h1>
    <div style="font-family:monospace;">
      0
    </div>
    <div style="font-family:monospace;">
      1
    </div>
    <div style="font-family:monospace;">
      2
    </div>
    <div data-hello="htmlgo">
    </div>
    <script>
      "alert('This is escaped');"
    </script>
    <script>
      alert("This is escaped");
    </script>
  </body>
</html>
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