string-replace-balanced is a CommonJS module exporting one class that encapsulates

• a pair of start / end tokens,
• a transform function

and contains a method to replace each ${start}${_}${end} fragment in a given string with the corresponding this.transform(_) value.

Installation

npm install string-replace-balanced

Usage

const TagProcessor = require ('string-replace-balanced')

const 
  template = '<*~one*> and <*~two*> makes 3.',
  val = {one: 1, two: 2},

// (1) bag of options

const processor = new TagProcessor ({
  start     : '<*~',
  end       :  '*>',
  transform : name => val [name]
})

// (2.1) subclass, setting properties via constructor

const processor = new (class extends TagProcessor {
  constructor () {
    super ()
    this.start = '<*~'
    this.end   =  '*>'
  }
  transform (_) {return val [_]}
})

// (2.2) subclass, implementing getters

const processor = new (class extends TagProcessor {
  get start  () {return '<*~'}
  get end    () {return '*>'}
  transform (_) {return val [_]}
})

// ...anyway,

console.log (processor.process (template))

// result: '1 and 2 makes 3.'

API

Constructor

The constructor takes a bag of options and copies its start, end and transform properties into 'this' instance. Neither option is mandatory, the argument may me omitted at all.

Properties

|Name | Type | Description |-|-|- |start | String | The opening bracket of tags to replace |end | String | The closing bracket of tags to replace

NOTE: It's the caller' responsibility to set start and end as non empty strings, an infinite loop may occur otherwise.

Methods

transform

This method, not implemented by default (but settable at instantiation via the bag of options) is called for each ${start}${_}${end} fragment with the _ value and must return the replacement string.

process

This method does the main job: takes a string and returns its copy with all ${start}${_}${end} fragments replaced.

Notes

The same functionality is available via the standard String.prototype.replaceAll() method, but only with regular expressions which cause a certain performance overhead, avoidable by using string-replace-balanced instead.

The original purpose of this module is to scan HTML for pictures given as Data URLs ("data:image ... ") and to store them separately overriding the corresponding links.

Limitations

No character escaping is supported: start and end are always considered tag delimiters and cannot be isolated with /*...*/, <![CDATA[...]]> nor whatever alike.

Nested tags are not allowed: each start is expected to be closed with the nearest end.

The balance is not enforced though. For example, multiple end tokens may occur in a row � they will be copied into the result as is without reporting an error.