Edge lexer
Generating high level tokens from Edge whitelisted markup
Edge lexer produces a list of tokens
by scanning for Edge whitelisted syntax.
This module is a blend of a lexer
and an AST generator
, since Edge doesn't need a pure lexer that scans for each character. Edge markup is written within other markup languages like HTML or Markdown and walking over each character is waste of resources.
Instead, this module starts with some REGEX patterns to detect the Edge whitelisted syntax and then starts the lexical analysis within the detected markup.
Performance
Following measures are taken to keep the analysis performant
- Only analyse markup that is detected as Edge whitelisted syntax.
- Only analyse
tags
, that are passed to the tokenizer. Which means even if the syntax for tags is whitelisted, the tokeniser will analyse them if they are used by your app. - Do not analyse Javascript expression and leave that for edge-parser.
Usage
import { Tokenizer } from 'edge-lexer'
const template = `Hello {{ username }}`
const tags = {
if: {
block: true,
selfclosed: false,
seekable: true
}
}
const options = {
filename: 'welcome.edge'
}
const tokenizer = new Tokenizer(template, tags, options)
tokenizer.parse()
console.log(tokenizer.tokens)
Features
- Allows multiline expressions.
- Whitespaces and newlines are retained.
- Detects for unclosed tags.
- Detects for unwrapped expressions and raises appropriate errors.
Terms used
This guide makes use of the following terms to identify core pieces of the tokenizer.
Term | Node Type | Description |
---|
Tag | block | Tags are used to define logical blocks in the template engine. For example if tag or include tag . |
Mustache | mustache | Javascript expression wrapped in curly braces. {{ }} |
Raw | raw | A raw string, which has no meaning for the template engine |
NewLine | newline | Newline |
Comment | comment | Edge specific comment block. This will be ripped off in the output. |
Nodes
Following is the list of Nodes returned by the tokenizer.
Block Node
{
type: 'block'
lineno: number,
properties: BlockProp,
children: []
}
Raw Node
{
type: 'raw',
lineno: number,
value: string
}
{
type: 'comment',
lineno: number,
value: string
}
Mustache Node
{
type: 'mustache',
lineno: number,
properties: Prop
}
NewLine Node
{
type: 'newline',
lineno: number
}
Key | Value | Description |
---|
type | string | The type of node determines the behavior of node |
lineno | number | The lineno in the source file |
properties | Prop | Meta data for the node. See Properties to more info. |
value | string | If node is a raw node, then value is the string in the source file |
children | array | Array of recursive nodes. Only exists, when type === 'block' . |
Properties
The properties Prop
is used to define meta data for a given Node. Nodes like raw
, comment
and newline
, doesn't need any metadata.
BlockProp
The block prop is used by the Block
node. The only difference from the regular Prop
is the addition of selfclosed
attribute.
{
name: string
jsArg: string,
raw: string,
selfclosed: boolean
}
Prop
{
name: string
jsArg: string,
raw: string
}
Key | Description |
---|
name | The name is the subtype for a given node. For example: if will be the name of the @if tag. |
jsArg | The jsArg is the Javascript expression to evaluate |
raw | The raw representation of a given expression. Used for debugging purposes. |
selfclosed | Whether or not the tag was selfclosed during usage. |
Mustache expressions
For mustache nodes props, the name
is the type of mustache expressions. The lexer supports 4 mustache expressions.
mustache
{{ username }}
e__mustache (Escaped mustache)
The following expression is ignored by edge. Helpful when you want this expression to be parsed by a frontend template engine
@{{ username }}
s__mustache (Safe mustache)
The following expression output is considered HTML safe.
{{{ '<p> Hello world </p>' }}}
es__mustache (Escaped safe mustache)
@{{{ '<p> Not touched </p>' }}}
Errors
Errors raised by the lexer
are always an instance of edge-error and will contain following properties.
error.message
error.line
error.col
error.filename
error.code
Example
@if(username)
<h2> Hello {{ username }} </h2>
@endif
The output of the above text will be
[
{
"type": "block",
"properties": {
"name": "if",
"jsArg": "username",
"raw": "if(username)",
"selfclosed": false
},
"lineno": 1,
"children": [
{
"type": "raw",
"value": "<h2> Hello ",
"lineno": 2
},
{
"type": "mustache",
"lineno": 2,
"properties": {
"name": "mustache",
"jsArg": " username ",
"raw": "<h2> Hello {{ username }} </h2>"
}
},
{
"type": "raw",
"value": " </h2>",
"lineno": 2
},
{
"type": "newline",
"lineno": 2
}
]
}
]
Change log
The change log can be found in the CHANGELOG.md file.
Contributing
Everyone is welcome to contribute. Please go through the following guides, before getting started.
- Contributing
- Code of conduct
Authors & License
thetutlage and contributors.
MIT License, see the included MIT file.