Jest throwing TypeError : this.inputEl.focus is not a function #1964

Question

Stencil version:

 @stencil/core@1.7.0

Jest version:

   "jest": "24.8.0"

Current behavior:

I am trying to focus a input element on button click. Which works fine, however upon trying to test the functionality using npm test , jest throws a TypeError saying focus is not a function.

This bug is being repeated for all the manual event invoke like click, blur, focus . Hence the test cases doesn't pass.

Expected behavior:

It should not throw error.

Steps to reproduce: I am providing a related demo code for inspection purpose. Related code:

demo-btn.tsx

import { Component, h, Element } from '@stencil/core';

@Component({
  tag: 'demo-btn',
  styleUrl: 'demo-btn.css',
  shadow: true
})
export class DemoBtnComponent {
  @Element() el!: HTMLElement;
  private inputEl?: HTMLElement;

  onClick = () => {
    if (this.inputEl) {
      this.inputEl.focus();
    }
  }

  render() {
    return (
      <div class="input-container">
        <input ref={el => this.inputEl = el} type="text" />
        <button onClick={this.onClick}>
          Click Me
      </button>
      </div>
    );
  }
}

demo-btn.spec.tsx

import { newSpecPage } from '@stencil/core/testing';
import { DemoBtnComponent } from './demo-btn';

describe('my-component', () => {
  it('should focus input el on btn click', async ()=> {
    const page = await newSpecPage({
      components: [DemoBtnComponent],
      html: '<demo-btn></demo-btn>',
    });

    const btn = page.root.shadowRoot.querySelector('button')
    btn.click(); // Throws error after this line
    await page.waitForChanges();
    expect(true).toBeTruthy(); // For sake of completion
  });
});

Any Help will be appreciated.

score 4 · Accepted Answer · answered Oct 23 '19 at 03:58

I Resolved this issue by mocking focus of input element. Below is the code I tried out:

import { newSpecPage } from '@stencil/core/testing';
import { DemoBtnComponent } from './demo-btn';

describe('my-component', () => {
  it('should focus input el on btn click', async ()=> {
    const page = await newSpecPage({
      components: [DemoBtnComponent],
      html: '<demo-btn></demo-btn>',
    });

    /** Mock Input Elements focus function */
    const inputEl = page.root.querySelector('input');
    inputEl.focus = jest.fn();


    const btn = page.root.querySelector('button')
    btn.click();
    await page.waitForChanges();
    expect(true).toBeTruthy();
  });
});

Closing this issue.

score 0 · Answer 2 · answered Mar 23 '22 at 18:55

I have faced the similar issue, however the above solution doesn't work if the focus() function is within a Lifecycle event. So, to fix this, I used optional chaining in the code itself:

this.inputEl?.focus?.();

More details in this article: https://github.com/ionic-team/stencil/issues/1964

Jest throwing TypeError : this.inputEl.focus is not a function #1964

2 Answers2