CODEWITHSUNDEEP
javascriptweb-componentstenciljs
Rosdi Kasim
Rosdi Kasim

Reputation: 26036

stenciljs Watch decorator not firing

I am trying to pass a JSON string to my component prop and let the component parse the string into javascript object.

Unfortunately the @Watch decorator is not firing... what did I do wrong? I followed this documentation: https://stenciljs.com/docs/reactive-data#watch-decorator

Here are the relevant parts of my code:

ptw-input.tsx

    import { Component, Prop, Watch } from "@stencil/core";

    @Component({
      tag: "ptw-input",
      styleUrl: "ptw-input.css",
      shadow: true
    })
    export class PtwInput {

      @Prop() data: string;

      innerData: any;

      @Watch('data')
      watchHandler(newValue: string): void {
        this.innerData = JSON.parse(newValue);
        console.log('this.innerData', this.innerData);
      }

      render(): JSX.Element {
        return (
          <input type="text" 
                 placeholder={this.innerData.placeholder}
                 disabled={this.innerData.disabled}
                 maxlength={this.innerData.maxlength}
        );
      }
    }

index.html 

    <head>
      <meta charset="utf-8">
      <meta name="viewport" content="width=device-width, initial-scale=1.0, minimum-scale=1.0, maximum-scale=5.0">
      <title>Stencil Component Starter</title>
      <script src="/build/ptw.js"></script>
    </head>

    <body>
        <ptw-input data='{"placeholder":"Type something", "disabled":false, "maxlength":4}'></ptw-input>
    </body>        
    </html>

... and here is my package.json

    {
      "name": "ptw-input",
      "version": "0.0.1",
      "description": "PTW input component",
      "module": "dist/esm/index.js",
      "main": "dist/index.js",
      "types": "dist/types/components.d.ts",
      "collection": "dist/collection/collection-manifest.json",
      "files": [
        "dist/"
      ],
      "scripts": {
        "build": "stencil build",
        "dev": "sd concurrent \"stencil build --dev --watch\" \"stencil-dev-server\" ",
        "serve": "stencil-dev-server",
        "start": "npm run dev",
        "test": "jest",
        "test.watch": "jest --watch"
      },
      "dependencies": {},
      "devDependencies": {
        "@stencil/core": "^0.9.11",
        "@stencil/dev-server": "latest",
        "@stencil/utils": "latest",
        "@types/jest": "^21.1.1",
        "jest": "^21.2.1"
      },
      "repository": {
        "type": "git",
        "url": "git+https://github.com/ionic-team/stencil-component-starter.git"
      },
      "author": "Ionic Team",
      "license": "MIT",
      "bugs": {
        "url": "https://github.com/ionic-team/stencil"
      },
      "homepage": "https://github.com/ionic-team/stencil",
      "jest": {
        "transform": {
          "^.+\\.(ts|tsx)$": "<rootDir>/node_modules/@stencil/core/testing/jest.preprocessor.js"
        },
        "testRegex": "(/__tests__/.*|\\.(test|spec))\\.(tsx?|jsx?)$",
        "moduleFileExtensions": [
          "ts",
          "tsx",
          "js",
          "json",
          "jsx"
        ]
      }
    }

I am using the latest stenciljs as shown in the package.json, but there is nothing in the console log except this error: TypeError: Cannot read property 'placeholder' of undefined

Upvotes: 2

Views: 5423

Answers (1)

matthewsteele
matthewsteele

Reputation: 1872

The @Watch decorator does not fire when a component initially loads.

To get the method to run when the component loads, invoke it inside a componentWillLoad lifecycle hook:

componentWillLoad() {
 this.watchHandler(this.newValue);
}

Upvotes: 11

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