Expand the prototype of HTMLElement

Question

Expand the prototype of HTMLElement

I'm attempting to enhance the prototype of the HTMLElement object in my main.ts file, with the intention of using it across my entire Angular 6 project.

However, I am encountering the error message:

Property 'fadeOut' does not exist on type 'HTMLElement'

.

HTMLElement.prototype.fadeOut = function(duration: number = 300): Promise<void> {
  const keyframes: AnimationKeyFrame[] = [{ opacity: 1 }, { opacity: 0 }];
  return new Promise(resolve => {
    const animation: Animation = this.animate(keyframes, duration);
    animation.onfinish = () => resolve();
  });
};

const circle = document.getElementById('circle');

HTMLElement.prototype.fadeOut = function(duration = 300) {
  const keyframes = [{ opacity: 1 }, { opacity: 0 }];
  return this.animate(keyframes, duration).finished
};

circle.fadeOut(2000);

#circle {
  height: 100px;
  width: 100px;
  margin: 50px;
  border-radius: 50%;
  background-color: #0f477f;
 }

<div id="circle"></>

What could be causing this issue?

Where should I place this code to ensure that the method is accessible globally?

Is there a way to refactor this code for improved clarity and efficiency?

javascript angular typescript

Answer 1

Answer №1

To ensure proper merging with the original interface, you must include a definition where you define an additional function to be added to the HTMLElement interface.

interface HTMLElement {
    fadeOut(duration: number): Promise<void>
}

// This will make it work
HTMLElement.prototype.fadeOut = function (duration: number = 300): Promise<void> {
    const keyframes: AnimationKeyFrame[] = [{ opacity: 1 }, { opacity: 0 }];
    return new Promise(resolve => {
        const animation: Animation = this.animate(keyframes, duration);
        animation.onfinish = () => resolve();
    });
};

If your code is within a module, remember to declare the interface in the global namespace.

declare global {
    interface HTMLElement {
        fadeOut(duration: number): Promise<void>
    }

}
HTMLElement.prototype.fadeOut = function (duration: number = 300): Promise<void> {
    const keyframes: AnimationKeyFrame[] = [{ opacity: 1 }, { opacity: 0 }];
    return new Promise(resolve => {
        const animation: Animation = this.animate(keyframes, duration);
        animation.onfinish = () => resolve();
    });
};


export var x;

Answer 2

To ensure proper merging with the original interface, you must include a definition where you define an additional function to be added to the HTMLElement interface.

interface HTMLElement {
    fadeOut(duration: number): Promise<void>
}

// This will make it work
HTMLElement.prototype.fadeOut = function (duration: number = 300): Promise<void> {
    const keyframes: AnimationKeyFrame[] = [{ opacity: 1 }, { opacity: 0 }];
    return new Promise(resolve => {
        const animation: Animation = this.animate(keyframes, duration);
        animation.onfinish = () => resolve();
    });
};

If your code is within a module, remember to declare the interface in the global namespace.

declare global {
    interface HTMLElement {
        fadeOut(duration: number): Promise<void>
    }

}
HTMLElement.prototype.fadeOut = function (duration: number = 300): Promise<void> {
    const keyframes: AnimationKeyFrame[] = [{ opacity: 1 }, { opacity: 0 }];
    return new Promise(resolve => {
        const animation: Animation = this.animate(keyframes, duration);
        animation.onfinish = () => resolve();
    });
};


export var x;

Expand the prototype of HTMLElement

Answer №1

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