Using SvelteKit and TypeScript to Manage Event Handling

Question

Using SvelteKit and TypeScript to Manage Event Handling

<script lang="ts">
    let statement = '0';

    function handleInput(event: MouseEvent) {
        let value = (event.currentTarget as HTMLElement).textContent
        if (statement === '0') {
            (statement = value);
        } else {
            (statement += statement);
        }
    }
</script>

<main class="container">
    <div class="calculator">
        <input type="text" class="calc__display" bind:value={expression} />
        <div class="calc__buttons">
            <button on:click={handleInput}>8</button>
            <button on:click={handleInput}>7</button>
            <button on:click={handleInput}>9</button>
            <button on:click={handleInput}>&divide</button>
        </div>
<!-- the rest of the buttons -->

(expression = value); - encountering an error: Type 'string | null' is not assignable to type 'string'. Type 'null' is not assignable to type 'string'.

Thus, when a user clicks on a button, it will activate the function handleInput(). This function's role is to update the content in .calc__display.

Any assistance provided would be greatly valued. Thank you!

typescript sveltekit

Answer 1

Answer №1

When encountering the error state, it is important to note that textContent may be null, making it unable to be assigned to a non-nullable type.

To address this issue, one could consider implementing a guard expression to check for this scenario or utilize a non-null assertion by appending an exclamation mark (!) at the end of the assignment.

Alternatively, a more efficient solution would be to pass the parameter directly to the function instead of retrieving data from the DOM, which is generally discouraged.

For example:

// ...
const expressions = ['8', '7', '9', '&divide'];

function onExpressionClick(ex: string) {
    if (expression === '0') {
        expression = ex;
    } else {
        // This action simply duplicates the expression, is this the intended behavior?
        expression += expression;
    }
}

Update buttons as follows:

{#each expressions as ex}
  <button on:click={() => onExpressionClick(ex)}>{ex}</button>
{/each}

Answer 2

When encountering the error state, it is important to note that textContent may be null, making it unable to be assigned to a non-nullable type.

To address this issue, one could consider implementing a guard expression to check for this scenario or utilize a non-null assertion by appending an exclamation mark (!) at the end of the assignment.

Alternatively, a more efficient solution would be to pass the parameter directly to the function instead of retrieving data from the DOM, which is generally discouraged.

For example:

// ...
const expressions = ['8', '7', '9', '&divide'];

function onExpressionClick(ex: string) {
    if (expression === '0') {
        expression = ex;
    } else {
        // This action simply duplicates the expression, is this the intended behavior?
        expression += expression;
    }
}

Update buttons as follows:

{#each expressions as ex}
  <button on:click={() => onExpressionClick(ex)}>{ex}</button>
{/each}

Using SvelteKit and TypeScript to Manage Event Handling

Answer №1

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