Use options to specify the caret position

Oct 13, 2025 by wbrum.org 146 views

When working with the typeIn function in Ember Headless Form, it's essential to understand its behavior, especially when it comes to preserving the caret position. In this article, we'll delve into the issue of typeIn not taking the caret position into account prior to inputting characters and explore the implications of this behavior.

Understanding the Issue

The problem arises when using the typeIn function to simulate user input in a form field. The function is designed to mimic the behavior of a user typing into the field, but it doesn't always preserve the caret position correctly. This can lead to unexpected test results, especially when the caret position changes based on the logic of the component being tested.

The Test Case

To illustrate this issue, let's take a look at a test case written for the LocalNumber component in Ember Headless Form. The test case is designed to verify that multiple decimals are handled correctly when typing into the field.

test("multiple decimals are handled", async function(assert) {
  const options = {
    style: "currency",
    currency: "USD"
  };

  await render(
    <template>
      <HeadlessForm as |form|>
        <form.Field @name="localNum" as |field|>
          <field.LocalNumber
            @locale="en-US"
            @formatOptions={{options}}
            @value="0.00"
          />
        </form.Field>
      </HeadlessForm>
    </template>
  );

  let input = this.element.querySelector("input") as HTMLInputElement;

  // For example, typing "123.45.67" should result in a properly formatted value.
  await typeIn("input", "12345");
  // $123.45|
  console.log(input.value);
  console.log(input.selectionStart);
  await typeIn("input", ".");
  // Should skip the caret to the decimal like so:
  // $123.|45
  console.log(input.value);
  console.log(input.selectionStart);
  await typeIn("input", "67");
  // The numbers should start pushing left. It should look like this:
  // $12,367.|45
  console.log(input.value);
  console.log(input.selectionStart);

  // Adjust the expected value to what your implementation should yield.
  assert.strictEqual(input.value, "$12,367.45", "Extra decimals are collapsed to a single decimal");
});

The Unexpected Behavior

When running this test case, the console output reveals an unexpected behavior. The caret position is not preserved correctly, and the input value is not formatted as expected.

test-app:test: not ok 53 Chrome 133.0 - [487 ms] - Integration Component HeadlessForm > Local Number: multiple decimals are handled
test-app:test:     ---
test-app:test:         actual: >
test-app:test:             $12,345.67
test-app:test:         expected: >
test-app:test:             $12,367.45
test-app:test:         stack: >
test-app:test:                 at Object.<anonymous> (http://localhost:4203/assets/tests.js:1833:14)
test-app:test:         message: >
test-app:test:             Extra decimals are collapsed to a single decimal
test-app:test:         negative: >
test-app:test:             false
test-app:test:         browser log: |
test-app:test:             {"type":"log","text":"$123.45"}
test-app:test:             {"type":"log","text":"7"}
test-app:test:             {"type":"log","text":"$123.45"}
test-app:test:             {"type":"log","text":"5"}
test-app:test:             {"type":"log","text":"$12,345.67"}
test-app:test:             {"type":"log","text":"10"}
test-app:test:     ...

Conclusion

In conclusion, the typeIn function in Ember Headless Form does not always preserve the caret position correctly. This can lead to unexpected test results, especially when the caret position changes based on the logic of the component being tested. To ensure accurate testing, it's essential to understand the behavior of typeIn and take steps to preserve the caret position correctly.

Recommendations

To address this issue, we recommend the following:

Review the typeIn function: Understand the behavior of typeIn and how it handles caret position.
Preserve caret position: Use techniques such as selectionStart and selectionEnd to preserve the caret position correctly.
Test thoroughly: Write comprehensive tests to ensure that the caret position is preserved correctly in all scenarios.

In our previous article, we explored the issue of typeIn not preserving the caret position correctly in Ember Headless Form. In this article, we'll answer some frequently asked questions related to this issue.

Q: What is the `typeIn` function in Ember Headless Form?

A: The typeIn function is a utility function in Ember Headless Form that simulates user input in a form field. It's designed to mimic the behavior of a user typing into the field, but it doesn't always preserve the caret position correctly.

Q: Why is the caret position not preserved correctly?

A: The caret position is not preserved correctly because the typeIn function doesn't take into account the current caret position when simulating user input. This can lead to unexpected behavior, especially when the caret position changes based on the logic of the component being tested.

Q: How can I preserve the caret position correctly?

A: To preserve the caret position correctly, you can use techniques such as selectionStart and selectionEnd to get and set the caret position. You can also use the typeIn function with options to specify the caret position.

Q: What are some common use cases where caret position preservation is important?

A: Caret position preservation is important in the following use cases:

Form validation: When validating form fields, it's essential to preserve the caret position to ensure that the user's input is not lost.
Autocomplete: When implementing autocomplete functionality, it's crucial to preserve the caret position to ensure that the user's input is not overwritten.
Dynamic content: When dynamically updating form fields, it's essential to preserve the caret position to ensure that the user's input is not lost.

Q: How can I test the caret position preservation correctly?

A: To test the caret position preservation correctly, you can write comprehensive tests that cover the following scenarios:

Initial caret position: Test that the initial caret position is preserved correctly.
User input: Test that the caret position is preserved correctly when the user inputs text.
Dynamic content: Test that the caret position is preserved correctly when dynamic content is updated.

Q: What are some best practices for using the `typeIn` function?

A: Here are some best practices for using the typeIn function:

Use options to specify the caret position: Use the typeIn function with options to specify the caret position.
Preserve the caret position correctly: Use techniques such as selectionStart and selectionEnd to preserve the caret position correctly.
Test thoroughly: Write comprehensive tests to ensure that the caret position is preserved correctly in all scenarios.

By following these best practices and testing thoroughly, you can ensure that your components behave correctly and provide a seamless user experience.