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kerosene-ui: Add measureCSSProperty function (#48)
* kerosene-ui: Add measureCSSProperty function * kerosene-ui: Bump version to 0.0.12
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| Original file line number | Diff line number | Diff line change |
|---|---|---|
| @@ -0,0 +1,54 @@ | ||
| import createSandbox from "jest-sandbox"; | ||
| import { when } from "jest-when"; | ||
| import measureCSSProperty from "./measureCSSProperty"; | ||
| import { JestMock } from "../../../kerosene-test/src"; | ||
|
|
||
| describe("measureCSSProperty", () => { | ||
| let sandbox: JestSandbox; | ||
| let createElement: JestMock<Document["createElement"]>; | ||
| let getComputedStyle: JestMock<Window["getComputedStyle"]>; | ||
| beforeEach(() => { | ||
| sandbox = createSandbox(); | ||
| createElement = jest.fn(); | ||
| document.createElement = createElement; | ||
| getComputedStyle = jest.fn(); | ||
| window.getComputedStyle = getComputedStyle; | ||
| }); | ||
|
|
||
| afterEach(() => { | ||
| sandbox.restore(); | ||
| }); | ||
|
|
||
| it("should inject a noscript tag and return the computed style", () => { | ||
| const el = { | ||
| appendChild: jest.fn(), | ||
| removeChild: jest.fn(), | ||
| }; | ||
|
|
||
| const noscript = { tagName: "NOSCRIPT", style: {} } as HTMLElement; | ||
| when(createElement) | ||
| .calledWith("noscript") | ||
| .mockReturnValue(noscript); | ||
|
|
||
| when(getComputedStyle) | ||
| .calledWith({ | ||
| ...noscript, | ||
| style: { ...noscript.style, paddingTop: "var(--header-height, 0px)" }, | ||
| } as HTMLElement) | ||
| .mockReturnValue({ paddingTop: "48px" } as CSSStyleDeclaration); | ||
|
|
||
| expect( | ||
| measureCSSProperty( | ||
| (el as Partial<Element>) as Element, | ||
| "paddingTop", | ||
| "var(--header-height, 0px)", | ||
| ), | ||
| ).toBe("48px"); | ||
| expect(el.appendChild).toBeCalledWith(noscript); | ||
| expect(noscript.style).toHaveProperty( | ||
| ["paddingTop"], | ||
| "var(--header-height, 0px)", | ||
| ); | ||
| expect(el.removeChild).toBeCalledWith(noscript); | ||
| }); | ||
| }); |
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| Original file line number | Diff line number | Diff line change |
|---|---|---|
| @@ -0,0 +1,38 @@ | ||
| /** | ||
| * Measures a CSS `property` at the provided `element` by injecting a `<noscript />` element and setting the style | ||
| * `property` to `value` and measuring with `window.getComputedStyle`. | ||
| * | ||
| * Useful for measuring CSS Custom Properties that contain calc expressions, e.g. | ||
| * | ||
| * ```css | ||
| * :root { | ||
| * --header-height: 48px; | ||
| * } | ||
| * | ||
| * @media only screen and (min-width: 768px) { | ||
| * :root { | ||
| * --header-height: 72px; | ||
| * } | ||
| * } | ||
| * ``` | ||
| * | ||
| * ```typescript | ||
| * const headerHeight = measureCSSProperty(document.body, "paddingTop", "var(--header-height, 0px)"); | ||
| * ``` | ||
| * | ||
| * @param element | ||
| * @param property | ||
| * @param value | ||
| */ | ||
| export default function measureCSSProperty<P extends keyof CSSStyleDeclaration>( | ||
| element: Element, | ||
| property: P, | ||
| value: CSSStyleDeclaration[P], | ||
| ): CSSStyleDeclaration[P] { | ||
| const noscript = document.createElement("noscript"); | ||
| noscript.style[property] = value; | ||
| element.appendChild(noscript); | ||
| const computed = window.getComputedStyle(noscript)[property]; | ||
| element.removeChild(noscript); | ||
| return computed; | ||
| } |
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