ts-lit-plugin
    TypeScript icon, indicating that this package has built-in type declarations

    1.2.1 • Public • Published

    ts-lit-plugin

    Typescript plugin that adds type checking and code completion to lit-html


    Downloads per month NPM Version Dependencies Contributors

    Lit plugin GIF

    -----------------------------------------------------

    ➤ Installation

    First, install the plugin:

    npm install ts-lit-plugin -D

    Then add a plugins section to your tsconfig.json:

    {
      "compilerOptions": {
        "plugins": [
          {
            "name": "ts-lit-plugin"
          }
        ]
      }
    }

    Finally, restart you Typescript Language Service, and you should start getting diagnostics from ts-lit-plugin.

    Note:

    • If you use Visual Studio Code you can also install the lit-plugin extension.
    • If you would rather use a CLI, you can install the lit-analyzer.

    -----------------------------------------------------

    ➤ Configuration

    You can configure this plugin through your tsconfig.json.

    Example

    {
      "compilerOptions": {
        "plugins": [
          {
            "name": "ts-lit-plugin",
            "strict": true,
            "rules": {
              "no-unknown-tag-name": "off",
              "no-unknown-event": "warn"
            }
          }
        ]
      }
    }

    Available options

    Option Description Type Default
    strict Enabling strict mode will change which rules are applied as default (see list of rules) boolean false
    rules Enable/disable individual rules or set their severity. Example: {"no-unknown-tag-name": "off"} {"rule-name": "off" \| "warn" \| "error"} The default rules enabled depend on the strict option
    disable Completely disable this plugin. boolean false
    dontShowSuggestions This option sets strict as boolean false
    htmlTemplateTags List of template tags to enable html support in. string[] ["html", "raw"]
    cssTemplateTags This option sets strict as string[] ["css"]
    globalTags List of html tag names that you expect to be present at all times. string[]
    globalAttributes List of html attributes names that you expect to be present at all times. string[]
    globalEvents List of event names that you expect to be present at all times string[]
    customHtmlData This plugin supports the custom vscode html data format through this setting. Vscode Custom HTML Data Format. Supports arrays, objects and relative file paths
    maxProjectImportDepth Determines how many modules deep dependencies are followed to determine whether a custom element is available in the current file. When -1 is used, dependencies will be followed infinitely deep. number -1
    maxNodeModuleImportDepth Determines how many modules deep dependencies in npm packages are followed to determine whether a custom element is available in the current file. When -1 is used, dependencies in npm packages will be followed infinitely deep. number 1

    -----------------------------------------------------

    ➤ Rules

    The default severity of each rule depend on the strict configuration option. Strict mode is disabled as default.

    Each rule can have severity of off, warning or error. You can toggle rules as you like.

    Validating custom elements

    Rule Description Severity normal Severity strict
    no-unknown-tag-name The existence of tag names are checked. Be aware that not all custom elements from libraries will be found out of the box. off warning
    no-missing-import When using custom elements in HTML it is checked if the element has been imported and is available in the current context. off warning
    no-unclosed-tag Unclosed tags, and invalid self closing tags like custom elements tags, are checked. warning error
    no-missing-element-type-definition This rule will ensure that custom elements are registered on the HTMLElementTagNameMap Typescript interface. off off

    Validating binding names

    Rule Description Severity normal Severity strict
    no-unknown-attribute
    no-unknown-property
    You will get a warning whenever you use an unknown attribute or property within your lit-html template. off warning
    no-unknown-event When using event bindings it's checked that the event names are fired. off off
    no-unknown-slot Using the "@slot" jsdoc tag on your custom element class, you can tell which slots are accepted for a particular element. off warning
    no-legacy-attribute Disallows use of legacy Polymer binding syntax (e.g. foo$=). off warning

    Validating binding types

    Rule Description Severity normal Severity strict
    no-invalid-boolean-binding Disallow boolean attribute bindings on non-boolean types. error error
    no-expressionless-property-binding Disallow property bindings without an expression. error error
    no-noncallable-event-binding Disallow event listener bindings with a noncallable type. error error
    no-boolean-in-attribute-binding Disallow attribute bindings with a boolean type. error error
    no-complex-attribute-binding Disallow attribute bindings with a complex type. error error
    no-nullable-attribute-binding Disallow attribute bindings with nullable types such as "null" or "undefined". error error
    no-incompatible-type-binding Disallow incompatible type in bindings. error error
    no-invalid-directive-binding Disallow using built-in directives in unsupported bindings. error error
    no-unintended-mixed-binding Disallow mixed value bindings where a character ', ", } or / is unintentionally included in the binding. warning warning

    Validating LitElement

    Rule Description Severity normal Severity strict
    no-incompatible-property-type When using the @property decorator in Typescript, the property option type is checked against the declared property Typescript type warn error
    no-invalid-attribute-name When using the property option attribute, the value is checked to make sure it's a valid attribute name. error error
    no-invalid-tag-name When defining a custom element the tag name is checked to make sure it's valid. error error
    no-property-visibility-mismatch This rule will ensure public properties use @property and non-public properties use @internalProperty. off warn

    Validating CSS

    Rule Description Severity normal Severity strict
    💅 no-invalid-css CSS within the tagged template literal css will be validated. warning error

    Validating custom elements

    All web components in your code are analyzed using web-component-analyzer which supports native custom elements and web components built with LitElement.

    🤷‍ no-unknown-tag-name

    Web components defined in libraries need to either extend the global HTMLElementTagNameMap (typescript definition file) or include the "@customElement tag-name" jsdoc on the custom element class.

    Below you will see an example of what to add to your library typescript definition files if you want type checking support for a given html tag name.

    declare global {
      interface HTMLElementTagNameMap {
        "my-element": MyElement;
      }
    }

    📣 no-missing-import

    When using custom elements in HTML it is checked if the element has been imported and is available in the current context. It's considered imported if any imported module (or their imports) defines the custom element.

    The following example is considered a warning:

    // No import of "my-element"
    html`<my-element></my-element>`

    The following example is not considered a warning:

    import "my-element.js";
    html`<my-element></my-element>`

    ☯ no-unclosed-tag

    Unclosed tags, and invalid self closing tags like custom elements tags, are checked.

    The following examples are considered warnings:

    html`<div>`
    html`<video />`
    html`<custom-element />`

    The following examples are not considered warnings:

    html`<div></div>`
    html`<custom-element></custom-element>`
    html`<video></video>`
    html`<input />`

    no-missing-element-type-definition

    This rule is only applicable to Typescript files.

    When sharing custom elements it's a good practice to add custom elements to the global interface HTMLElementTagNameMap. This rule will ensure that custom elements are registered on this interface.

    The following example is considered a warning:

    export class MyElement extends HTMLElement {
     
    } 
     
    customElements.define("my-element", MyElement)

    The following example is not considered a warning:

    export class MyElement extends HTMLElement {
     
    } 
     
    customElements.define("my-element", MyElement)
     
    declare global {
      interface HTMLElementTagNameMap {
        "my-element": MyElement
      }
    }

    Validating binding names

    Attributes, properties and events are picked up on custom elements using web-component-analyzer which supports native custom elements and web components built with LitElement.

    ✅ no-unknown-attribute, no-unknown-property

    You will get a warning whenever you use an unknown attribute or property. This check is made on both custom elements and built in elements.

    The following example is considered a warning:

    html`<input .valuuue="${value}" unknownattribute="button" />`

    The following example is not considered a warning:

    html`<input .value="${value}" type="button" />`

    ⚡️ no-unknown-event

    You can opt in to check for unknown event names. Using the @fires jsdoc or the statement this.dispatch(new CustomEvent("my-event)) will make the event name available. All event names are accepted globally because events bubble.

    The following example is considered a warning:

    html`<input @iinput="${console.log}" />`

    The following example is not considered a warning:

    html`<input @input="${console.log}" />`

    📬 no-unknown-slot

    Using the "@slot" jsdoc tag on your custom element class, you can tell which slots are accepted for a particular element. Then you will get warnings for invalid slot names and if you forget to add the slot attribute on elements without an unnamed slot.

    /**
     * @slot - This is a comment for the unnamed slot
     * @slot right - Right content
     * @slot left
     */
    class MyElement extends HTMLElement {
    }
    customElements.define("my-element", MyElement);

    The following example is considered a warning:

    html`
    <my-element>
      <div slot="not a slot name"></div>
    </my-element>
    `

    The following example is not considered a warning:

    html`
    <my-element>
      <div></div>
      <div slot="right"></div>
      <div slot="left"></div>
    </my-element>
    `

    no-legacy-attribute

    A common mistake when dealing with Lit in particular is to use the legacy Polymer syntax as seen in earlier versions of Polymer (the predecessor of Lit).

    The following examples are considered warnings:

    html`<input name$=${val} />`
    html`<input disabled?=${val} />`;
    html`<input name="val" />`;

    The following examples are not considered warnings:

    html`<input name=${val} />`
    html`<input ?disabled=${val} />`;
    html`<input name=${val} />`;

    Validating binding types

    Be aware that many checks involving analyzing bindings will work better in Typescript files because we have more information about the values being bound.

    ❓ no-invalid-boolean-binding

    It never makes sense to use the boolean attribute binding on a non-boolean type.

    The following example is considered a warning:

    html`<input ?type="${"button"}" />`

    The following example is not considered a warning:

    html`<input ?disabled="${isDisabled}" />`

    ⚫️ no-expressionless-property-binding

    Because of how lit-html parses bindings internally you cannot use the property binding without an expression.

    The following example is considered a warning:

    html`<input .value="text" />`

    The following example is not considered a warning:

    html`<input .value="${text}" />`

    🌀 no-noncallable-event-binding

    It's a common mistake to incorrectly call the function when setting up an event handler binding instead of passing a reference to the function. This makes the function call whenever the code evaluates.

    The following examples are considered warnings:

    html`<button @click="${myEventHandler()}">Click</button>`
    html`<button @click="${{hannndleEvent: console.log()}}">Click</button>`

    The following examples are not considered warnings:

    html`<button @click="${myEventHandler}">Click</button>`
    html`<button @click="${{handleEvent: console.log}}">Click</button>`

    😈 no-boolean-in-attribute-binding

    You should not be binding to a boolean type using an attribute binding because it could result in binding the string "true" or "false". Instead you should be using a boolean attribute binding.

    This error is particular tricky, because the string "false" is truthy when evaluated in a conditional.

    The following example is considered a warning:

    html`<input disabled="${isDisabled}" />`

    The following example is not considered a warning:

    html`<input ?disabled="${isDisabled}" />`

    ☢️ no-complex-attribute-binding

    Binding an object using an attribute binding would result in binding the string "[object Object]" to the attribute. In this cases it's probably better to use a property binding instead.

    The following example is considered a warning:

    html`<my-list listitems="${listItems}"></my-list>`

    The following example is not considered a warning:

    html`<my-list .listItems="${listItems}"></my-list>`

    ⭕️ no-nullable-attribute-binding

    Binding undefined or null in an attribute binding will result in binding the string "undefined" or "null". Here you should probably wrap your expression in the "ifDefined" directive.

    The following examples are considered warnings:

    html`<input value="${maybeUndefined}" />`
    html`<input value="${maybeNull}" />`

    The following examples are not considered warnings:

    html`<input value="${ifDefined(maybeUndefined)}" />`
    html`<input value="${ifDefined(maybeNull === null ? undefined : maybeNull)}" />`

    💔 no-incompatible-type-binding

    Assignments in your HTML are typed checked just like it would be in Typescript.

    The following examples are considered warnings:

    html`<input type="wrongvalue" />`
    html`<input placeholder />`
    html`<input max="${"hello"}" />`
    html`<my-list .listItems="${123}"></my-list>`

    The following examples are not considered warnings:

    html`<input type="button" />`
    html`<input placeholder="a placeholder" />`
    html`<input max="${123}" />`
    html`<my-list .listItems="${listItems}"></my-list>`

    💥 no-invalid-directive-binding

    Directives are checked to make sure that the following rules are met:

    • ifDefined is only used in an attribute binding.
    • class is only used in an attribute binding on the 'class' attribute.
    • style is only used in an attribute binding on the 'style' attribute.
    • unsafeHTML, cache, repeat, asyncReplace and asyncAppend are only used within a text binding.

    The directives already make these checks on runtime, so this will help you catch errors before runtime.

    The following examples are considered warnings:

    html`<input value="${unsafeHTML(html)}" />`
    html`<input .value="${ifDefined(myValue)}" />`
    html`<div role="${class(classMap)}"></div>`

    The following examples are not considered warnings:

    html`<button>${unsafeHTML(html)}</button>`
    html`<input .value="${myValue}" />`
    html`<input value="${myValue}" />`
    html`<div class="${class(classMap)}"></div>`

    🕷 no-unintended-mixed-binding

    Sometimes unintended characters sneak into bindings. This often indicates a typo such as <input value=${"foo"}} /> where the expression is directly followed by a "}" which will be included in the value being bound, resulting in "foo}". Another example is self-closing tags without a space between the binding and "/" like <input value=${"foo"}/> which will result in binding the string "myvalue/".

    This rule disallows mixed value bindings where a character ', ", } or / is unintentionally included in the binding.

    The following examples are considered warnings:

    html`<input .value=${"myvalue"}" />`
    html`<input value=${"myvalue"}} />`
    html`<input value=${"myvalue"}/>`
    html`<input ?required=${true}/>`

    The following examples are not considered warnings:

    html`<input .value=${"myvalue"} />`
    html`<input value="${"myvalue"}" />`
    html`<input ?required=${true} />`
    html`<input @input="${console.log}" />`

    Validating LitElement

    💞 no-incompatible-property-type

    This rule checks that LitElement-controlled properties are correctly configured in accordance with the default value converter.

    The following is a summary of what this rule does:

    1. The type given to the LitElement property configuration is checked against the actual Typescript type of the property.
    2. The default converter only accepts the types String, Boolean, Number, Array and Object, so all other values for type are considered warnings.
    3. The absence of a type is only considered a warning if the property is not assignable to the string type.

    This rule will not check for a given LitElement-controlled property if the property has custom converter configured.

    The following examples are considered warnings:

    class MyElement extends LitElement {
      @property({type: Number}) text: string;
      @property({type: Boolean}) count: number;
      @property({type: String}) disabled: boolean;
      @property({type: Object}) list: ListItem[];
     
      static get properties () {
        return {
          callback: {
            type: Function
          },
          text: {
            type: MyElement
          }
        }
      }
    }

    The following examples are not considered warnings:

    class MyElement extends LitElement {
      @property({type: String}) text: string;
      @property({type: Number}) count: number;
      @property({type: Boolean}) disabled: boolean;
      @property({type: Array}) list: ListItem[];
     
      static get properties () {
        return {
          callback: {
            type: Function,
            converter: myCustomConverter
          },
          text: {
            type: String
          }
        }
      }
     
    }

    ⁉️ no-invalid-attribute-name

    When using the property option attribute, the value is checked to make sure it's a valid attribute name.

    The following example is considered a warning:

    class MyElement extends LitElement {
      static get properties () {
        return {
          text: {
            attribute: "invald=name"
          }
        }
      }
    }

    ⁉️ no-invalid-tag-name

    When defining a custom element, the tag name is checked to make sure it's a valid custom element name.

    The following example is considered a warning:

    @customElement("wrongElementName")
    class MyElement extends LitElement {
    }
     
    customElements.define("alsoWrongName", MyElement);

    The following example is not considered a warning:

    @customElement("my-element")
    class MyElement extends LitElement {
    }
     
    customElements.define("correct-element-name", MyElement);

    no-property-visibility-mismatch

    When using the @property decorator, your property should be publicly visible, expected to be exposed to consumers of the element. Private and protected properties however, should make use of the @internalProperty decorator instead.

    This rule will ensure public properties use @property and non-public properties use @internalProperty.

    The following example is considered a warning:

    class MyElement extends LitElement {
        @property() private myProperty: string;
    }

    Validating CSS

    lit-analyzer uses vscode-css-languageservice to validate CSS.

    💅 no-invalid-css

    CSS within the tagged template literal css will be validated.

    The following example is considered a warning:

    css`
      button
        background: red;
      }
    `

    The following example is not considered a warning:

    css`
      button {
        background: red;
      }
    `

    -----------------------------------------------------

    ➤ Documenting slots, events, attributes and properties

    Code is analyzed using web-component-analyzer in order to find properties, attributes and events. Unfortunately, sometimes it's not possible to analyze these things by looking at the code, and you will have to document how your component looks using jsdoclike this:

    /**
     * This is my element
     * @attr size
     * @attr {red|blue} color - The color of my element
     * @prop {String} value
     * @prop {Boolean} myProp - This is my property
     * @fires change
     * @fires my-event - This is my own event
     * @slot - This is a comment for the unnamed slot
     * @slot right - Right content
     * @slot left
     * @cssprop {Color} --border-color
     * @csspart header
     */
    class MyElement extends HTMLElement { 
    }
     
    customElements.define("my-element", MyElement);

    -----------------------------------------------------

    ➤ Contributors

    Rune Mehlsen Andreas Mehlsen You?
    Rune Mehlsen Andreas Mehlsen You?

    -----------------------------------------------------

    ➤ License

    Licensed under MIT.

    Install

    npm i ts-lit-plugin

    DownloadsWeekly Downloads

    5,587

    Version

    1.2.1

    License

    MIT

    Unpacked Size

    92.3 kB

    Total Files

    62

    Last publish

    Collaborators

    • runebm