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Fix type assertion #3

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Merged
merged 5 commits into from
Dec 2, 2021
Merged

Fix type assertion #3

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f45c958
fix: correct type assertion for isElement
JounQin Oct 21, 2021
fa78914
chore: address review comments
JounQin Dec 1, 2021
814b4b4
chore: simply types
JounQin Dec 1, 2021
98d7062
Update index.test-d.ts
JounQin Dec 1, 2021
068fd85
Update index.test-d.ts
JounQin Dec 1, 2021
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11 changes: 9 additions & 2 deletions index.js
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Original file line number Diff line number Diff line change
Expand Up @@ -7,6 +7,11 @@
* @typedef {null|undefined|TagName|TestFunctionAnything|Array.<TagName|TestFunctionAnything>} Test
*/

/**
* @template {Element} T
* @typedef {null|undefined|T['tagName']|TestFunctionPredicate<T>|Array.<T['tagName']|TestFunctionPredicate<T>>} PredicateTest
*/

/**
* Check if an element passes a test
*
Expand Down Expand Up @@ -56,8 +61,10 @@ export const isElement =
* When a `parent` node is known the `index` of node should also be given.
*
* @type {(
* (<T extends Element>(node: unknown, test: T['tagName']|TestFunctionPredicate<T>|Array.<T['tagName']|TestFunctionPredicate<T>>, index?: number, parent?: Parent, context?: unknown) => node is T) &
* ((node?: unknown, test?: Test, index?: number, parent?: Parent, context?: unknown) => boolean)
* (() => false) &
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I still think we should remove this in typings.

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What is the benefit in removing it?
The benefit in having it is that it matches how the code works. Generally, types should match the code. Why deviate from the code and introduce a breaking change?

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@JounQin JounQin Dec 1, 2021 •
edited
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Generally, types should match the code.

TypeScript should be stricter than codes, the benefit is that isElement() is always meaningless in practice, and you should not use it at all. For example, parseInt(num) or parseInt() are valid in js, but error in ts.

introduce a breaking change

Personally, I won't say updating better practice types as breaking change.

* (<T extends Element>(node: unknown, test: PredicateTest<T>, index?: number, parent?: Parent, context?: unknown) => node is T) &
* ((node: unknown, test?: PredicateTest<Element>, index?: number, parent?: Parent, context?: unknown) => node is Element) &
* ((node: unknown, test: Test, index?: number, parent?: Parent, context?: unknown) => boolean)
* )}
*/
(
Expand Down
31 changes: 30 additions & 1 deletion index.test-d.ts
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Original file line number Diff line number Diff line change
Expand Up @@ -30,7 +30,7 @@ const article: Element = {
const isSection = (element: Element): element is Section =>
element.tagName === 'section'

isElement()
expectType<false>(isElement())

/* Missing parameters. */
expectError(isElement<Section>())
Expand Down Expand Up @@ -133,3 +133,32 @@ convertElement()
convertElement(null)
convertElement(undefined)
expectError(convertElement<Article>())

declare const node: unknown

/* Type assertion */
if (isElement(node)) {
expectType<Element>(node)
}

if (
isElement<Section>(
node,
(node): node is Section => 'tagName' in node && node.tagName === 'section'
)
) {
expectType<Section>(node)
}

if (isElement(node, node => 'children' in node)) {
expectType<unknown>(node)
} else {
expectType<unknown>(node)
}


if (isElement(node) && 'children' in node) {
expectType<Element>(node)
} else {
expectType<unknown>(node)
}