Created
October 9, 2022 10:53
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| /** | |
| * Get absolute xy position of caret in px. | |
| * Time to execute: ~2.5ms on a 2018 MacBook Pro. | |
| * Inpired by: https://medium.com/@jh3y/how-to-where-s-the-caret-getting-the-xy-position-of-the-caret-a24ba372990a | |
| * @param {object} element - the textarea element to obtain coordinates for | |
| */ | |
| export function getCaretXY(element: HTMLTextAreaElement): { x: number, top: number, bottom: number } { | |
| const { top: textElementTop, left: textElementLeft } = element.getBoundingClientRect() | |
| const selectionPoint = element.selectionEnd | |
| // Create a dummy element, copy style and populate with content up to the caret. | |
| const dummy = document.createElement('div') | |
| const computedStyle = getComputedStyle(element) | |
| for (const prop of computedStyle) { | |
| dummy.style[prop] = computedStyle[prop] | |
| } | |
| dummy.textContent = element.value.substring(0, selectionPoint) | |
| dummy.style.position = 'relative' // this is important to get the relative position of the div. | |
| dummy.style.height = 'auto' | |
| // Add a marker element to obtain relative caret position. | |
| const span = document.createElement('span') | |
| span.textContent = '' | |
| dummy.appendChild(span) | |
| document.body.appendChild(dummy) | |
| const { | |
| offsetLeft: caretElementOffLeft, | |
| offsetTop: caretElementOffTop, | |
| offsetHeight: caretElementHeight, | |
| } = span | |
| // Remove the dummy element. | |
| document.body.removeChild(dummy) | |
| return { | |
| x: textElementLeft + caretElementOffLeft, // Width is 0px. | |
| top: textElementTop + caretElementOffTop, | |
| bottom: textElementTop + caretElementOffTop + caretElementHeight, | |
| } | |
| } |
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