Blame · textareaUtils.tsx

b69ab31	1	/**
b69ab31	2	* Copyright (c) Meta Platforms, Inc. and affiliates.
b69ab31	3	*
b69ab31	4	* This source code is licensed under the MIT license found in the
b69ab31	5	* LICENSE file in the root directory of this source tree.
b69ab31	6	*/
b69ab31	7
b69ab31	8	/**
b69ab31	9	* Replace text in a text area.
b69ab31	10	* Re-adjust cursor & selection to be the same as before the replacement.
b69ab31	11	*/
b69ab31	12	export function replaceInTextArea(textArea: HTMLTextAreaElement, oldText: string, newText: string) {
b69ab31	13	const {selectionStart, selectionEnd} = textArea;
b69ab31	14	const insertionSpot = textArea.value.indexOf(oldText);
b69ab31	15	textArea.value = textArea.value.replace(oldText, newText);
b69ab31	16	// re-select whatever we had selected before.
b69ab31	17	// if the new text is longer, we may need to add additional length
b69ab31	18	if (selectionStart) {
b69ab31	19	textArea.selectionStart =
b69ab31	20	selectionStart > insertionSpot
b69ab31	21	? selectionStart + (newText.length - oldText.length)
b69ab31	22	: selectionStart;
b69ab31	23	}
b69ab31	24	if (selectionEnd) {
b69ab31	25	textArea.selectionEnd =
b69ab31	26	selectionEnd > insertionSpot
b69ab31	27	? selectionEnd + (newText.length - oldText.length)
b69ab31	28	: selectionEnd;
b69ab31	29	}
b69ab31	30	}
b69ab31	31
b69ab31	32	/**
b69ab31	33	* Insert text into a text area at the cursor location.
b69ab31	34	* Add spaces before/after as necessary so the new text does not neighbor the existing content.
b69ab31	35	* If text is selected, replace the selected text with the new text.
b69ab31	36	* If nothing is selected, append to the end.
b69ab31	37	*/
b69ab31	38	export function insertAtCursor(textArea: HTMLTextAreaElement, text: string) {
b69ab31	39	if (textArea.selectionStart != null) {
b69ab31	40	const startPos = textArea.selectionStart;
b69ab31	41	const endPos = textArea.selectionEnd;
b69ab31	42	const nextCharPos = endPos ?? startPos;
b69ab31	43	const previousChar = textArea.value[startPos - 1];
b69ab31	44	const nextChar = textArea.value[nextCharPos];
b69ab31	45	const isWhitespace = (s: string \| undefined) => !s \|\| /[ \n\t]/.test(s);
b69ab31	46	// if inserting next to whitespace, no need to add more.
b69ab31	47	// if inserting next to text, add a space before to avoid the link becoming invalid.
b69ab31	48	const prefix = isWhitespace(previousChar) ? '' : ' ';
b69ab31	49	// similarly for suffix
b69ab31	50	const suffix = isWhitespace(nextChar) ? '' : ' ';
b69ab31	51	const totalAddedLength = text.length + prefix.length + suffix.length;
b69ab31	52	textArea.value =
b69ab31	53	textArea.value.substring(0, startPos) +
b69ab31	54	prefix +
b69ab31	55	text +
b69ab31	56	suffix +
b69ab31	57	(endPos != null ? textArea.value.substring(endPos, textArea.value.length) : '');
b69ab31	58	const newPos = startPos + totalAddedLength;
b69ab31	59	textArea.selectionStart = newPos;
b69ab31	60	textArea.selectionEnd = newPos;
b69ab31	61	} else {
b69ab31	62	// no selection => append to the end
b69ab31	63	const prefix = /\s/.test(textArea.value[textArea.value.length - 1]) ? '' : ' ';
b69ab31	64	textArea.value += prefix + text;
b69ab31	65	}
b69ab31	66	}