Lex.js

> A preact-based micro-framework for building token-based search bars

Introduction

Lex is a micro-framework for building token-based search bars. Rather than predefining how searches are performed, Lex provides developers with the tools they need to define their own query language, and to develop unique UI components for constructing queries, thus supporting the widest possible set of potential use cases.

Lex is built internally with Preact, ensuring a minimal library size and compatibility with any modern SPA framework (VueJS, Aurelia, React, etc.) by remaining framework-neutral.

API Documentation and Demos

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For current API documentation, please visit: https://unchartedsoftware.github.io/lex/

For demos of key features, visit: https://unchartedsoftware.github.io/lex/demo/

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For current API documentation, please clone the project and run:

``bash
$ npm install
$ npm run serve-docs
`

For demos of key features, refer to source in the demo directory, while running:

`bash
$ npm install
$ npm run serve-demos
`

Using Lex

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> In Lex, a search language is a finite-state machine. States represent "steps" towards successfully constructing a token through user-supplied values, and users transition() between them until they reach a terminal State (one with no children).

Lex attempts to provide an environment in which developers can craft their own search language, rather than enforcing one. Despite this goal, the following assumptions are made for the sake of improving user experience:

1. A query consists of a list of tokens (i.e. [TOKEN1 TOKEN2 TOKEN3])
1. The set of tokens in a Lex bar is interpeted as being joined by either ANDs or ORs (i.e. [TOKEN1 & TOKEN2 & TOKEN3]). This connective is not represented visually within the search bar, and thus is left up to the interpretation of the developer (however so far all existing apps using Lex have chosen AND).
1. Tokens consist of a list of States - effectively, a path through the search language. Each State stores one or more values and, together, the sequence represents a statement such as [Name, is, Sean], [Age, is not, 7] or [Location, is, (Toronto,Victoria)].
1. Multi-value States can represent an OR of values which, together with an overall choice of AND connective, strongly encourage Conjunctive Normal Form as the basis for a search language.

Defining a search language in Lex is accomplished via method chaining. Let's start with a basic search language, which allows a user to select a column to search and supply a value. The state machine for this language consists of three states, with specific rules governing the transition between the root state and its two children:

`
Choose Column ----(if string)----> Enter String
\---(if numeric)---> Enter Number
`

Here is the implementation via Lex:

`js
import { Lex, TransitionFactory, ValueState, ValueStateValue, TextEntryState, NumericEntryState } from 'lex';;

// Lex.from() starts a subtree of the language
const language = Lex.from('columnName', ValueState, {
name: 'Choose a column to search',
suggestions: [
// ValueStates allow users to choose from a list
// of values (or potentially create their own).
// We set metadata "type"s on these options
// to help us make transition decisions later.
new ValueStateValue('Name', {type: 'string'}),
new ValueStateValue('Age', {type: 'numeric'})
]
}).branch(
Lex.from('value', TextEntryState, {
// transitions to this State are considered legal
// if the parent State's value had a metadata
// type === 'string'
...TransitionFactory.valueMetaCompare({type: 'string'})
}),
Lex.from('value', NumericEntryState, {
// Similarly, checking for parentVal.meta.type === 'numeric'
...TransitionFactory.valueMetaCompare({type: 'numeric'})
}),
);
`

Consuming the language is as accomplished via configuration when constructing a new instance of Lex.

`js
// Now we can instantiate a search bar that will respect this language.
const lex = new Lex({
language: language
// other configuration goes here
});
lex.render(document.getElementById('LexContainer'));
`

Lex supports far more complex languages, validation rules, state types etc. than are shown in this brief example. Check out the demo directory and API documentation for more details.

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Lex translates States from the search language into UI components as a user is creating or modifying a Token. These components fall into two categories:

1. Builders - UI which is presented inline within a Token. This is generally a text input that the user can type into to supply values to the current State.
1. Assistants - UI which is presented as a drop-down below a Token. Assistants provide an alternative, typically richer, mechanism for supplying values to the current State.

There must be one Builder for each State in a search language. Assistants are optional.

Lex contains several built-in State types, which are associated with default Builders and Assistants:

State | Default Builder | Default Assistant
------ | --------------- | -----------------
LabelState | LabelBuilder | none
ValueState | ValueBuilder | ValueAssistant
RelationState | ValueBuilder | ValueAssistant
TerminalState | TerminalBuilder | none
TextEntryState | ValueBuilder | ValueAssistant
TextRelationState | ValueBuilder | ValueAssistant
NumericEntryState | ValueBuilder | ValueAssistant
NumericRelationState | ValueBuilder | ValueAssistant
CurrencyEntryState | ValueBuilder | ValueAssistant
DateTimeEntryState | DateTimeEntryBuilder | DateTimeEntryAssistant
DateTimeRelationState | ValueBuilder | ValueAssistant

Two things are evident in this table:

1. Most State types extend ValueState, which is a powerful component supporting selecting a value from a list of suggestions, entering custom values, accepting multiple values, etc.
1. Any State type which is missing a direct Builder or Assistant will attempt to use the corresponding components for its superclass State.

Lex may be extended, therefore, in the following ways (in descending order of likelihood):

1. Via the implementation of new States, extending existing States (i.e. extending ValueState but using ValueBuilder and ValueAssistant)
1. Via the implementation of new Assistants for existing States (i.e. implementing a custom drop-down UI for choosing dates and times)
1. Via the implementation of new Builders for existing States (mostly for formatting "finished" Tokens in unique ways by overriding renderReadOnly())
1. Via the implementation of entirely unique States, with custom Builders and Assistants. (i.e. implementing a GeoBoundsEntryState with a custom Builder, and an Assistant featuring a map)

The States, Builders and Assistants within the library are well-documented examples of how these extension types are accomplished, and exist as a reference for this purpose.

Overrides must be registered with Lex before the search bar is rendered:

`js
// ...
lex.registerBuilder(DateTimeEntryState, CustomDateTimeEntryBuilder);
lex.registerAssistant(CurrencyEntryState, CustomCurrencyEntryAssistant);
lex.render(document.getElementById('LexContainer'));
`

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The following co-requisites must be part of your JS build in order to use Lex:

`js
{
"element-resize-detector": "1.1.x", // developed against "1.1.15"
"preact": "8.x", // developed against: "8.5.2",
"moment-timezone": "0.5.x", // developed against "0.5.34"
"flatpickr": "4.6.x" // developed against: "4.6.3"
}
``

The following polyfills are required for use in IE and are not provided by this library:

- ES6 Promise Polyfill