What could be preventing data from properly binding to my AngularJS component?

I want to create an AngularJS component called messageDisplay. This component should be able to accept a property named message, which will be provided directly in the HTML tag of the index.html file, and then display that message. Despite following various examples, I'm unable to get it to work as expected.

index.html

<!DOCTYPE html>
<html>

    <head>
        <meta charset="utf-8" />
        <title>Angular sandbox</title>
        <script src="https://ajax.googleapis.com/ajax/libs/angularjs/1.5.6/angular.js"></script>
        <script src="app.js"></script>
        <script src="components/message-display.component.js"></script>
    </head>

    <body ng-app="app">
        <message-display message="Hello"></message-display>
    </body>

</html>

app.js

const app = angular.module("app", []);

message-display.component.js

app.component(
        "messageDisplay",
        {
            bindings: {
                message: "<"
            },
            template: "<h1>Message: {{$ctrl.message}}</h1>"
        }
    )

When I try this setup, all I see on the page is "Message:" without the actual content. I was expecting to see "Message: Hello".

Answer №1

When passing strings to one-way ("<") bindings, remember to use single quotes:

<message-display message="'Hi'"></message-display>

Otherwise, it will be interpreted as an AngularJS expression, such as $scope.Hi

The DEMO

angular.module("app",[])
.component(
        "messageDisplay",
        {
            bindings: {
                message: "<"
            },
            template: "<h1>Message: {{$ctrl.message}}</h1>"
        }
)
<script src="//unpkg.com/angular/angular.js"></script>
<body ng-app="app">
        <message-display message="'Hi'"></message-display>
</body>


Update

If you are looking to learn more about the "bindings" concept and the symbols like <, &, =, @, I would recommend checking out the following resources:

For additional information, please visit:

In my experience, I tend to avoid two-way ("=") binding as it can complicate the transition to Angular 2+.

Similarly, I steer clear of attribute ("@") binding for consistency reasons. This way, I don't have to differentiate between attributes that require an AngularJS expression versus those that need mustaches ({{ }}).

Answer №2

Hello, for proper binding use '@' as shown below:

app.component(
        "displayMessage",
        {
            bindings: {
                content: "@"
            },
            template: "<h1>Content: {{$ctrl.content}}</h1>"
        }
    )

Answer №3

  1. < Single-way Data Binding: This occurs when we only need to access a parameter from a parent scope without updating it.
  2. @ is used for String Parameters.

const app = angular.module("app", []);
  app.component(
        "messageDisplay",
        {
              bindings: {
                message: "@"
              },
              template: "<h1>Message: {{$ctrl.message}}</h1>"
        }
    )
<!doctype html>
<html>
  <head>
    <script src="https://ajax.googleapis.com/ajax/libs/angularjs/1.7.2/angular.min.js"></script>
  
  </head>
  <body ng-app="app">
        <message-display message="Hi"></message-display>
    </body>
</html>

<!-- 
Copyright 2018 Google Inc. All Rights Reserved.
Use of this source code is governed by an MIT-style license that
can be found in the LICENSE file at https://angular.io/license
-->

For more information, visit the blog post here ->

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