type TextAreaHeight = { height: string minHeight?: string } type NodeStyle = { contextStyle: string boxSizing: string paddingSize: number borderSize: number } let hiddenTextarea: HTMLElement const HIDDEN_STYLE = ` height:0 !important; visibility:hidden !important; overflow:hidden !important; position:absolute !important; z-index:-1000 !important; top:0 !important; right:0 !important; ` const CONTEXT_STYLE = [ 'letter-spacing', 'line-height', 'padding-top', 'padding-bottom', 'font-family', 'font-weight', 'font-size', 'text-rendering', 'text-transform', 'width', 'text-indent', 'padding-left', 'padding-right', 'border-width', 'box-sizing', ] function calculateNodeStyling(targetElement: HTMLTextAreaElement): NodeStyle { const style = window.getComputedStyle(targetElement) const boxSizing = style.getPropertyPriority('box-sizing') const paddingSize = (parseFloat(style.getPropertyPriority('padding-bottom')) + parseFloat(style.getPropertyPriority('padding-top'))) || 0 const borderSize = parseFloat(style.getPropertyValue('border-bottom-width')) + parseFloat(style.getPropertyValue('border-top-width')) || 0 const contextStyle = CONTEXT_STYLE.map(name => `${name}:${style.getPropertyValue(name)}`).join(';') return { contextStyle, paddingSize, borderSize, boxSizing } } export default function calcTextareaHeight( targetElement: HTMLTextAreaElement, minRows = 1, maxRows = null, ): TextAreaHeight { if (!hiddenTextarea) { hiddenTextarea = document.createElement('textarea') document.body.appendChild(hiddenTextarea) } const { paddingSize, borderSize, boxSizing, contextStyle } = calculateNodeStyling(targetElement) console.log(paddingSize, borderSize, boxSizing, contextStyle) hiddenTextarea.setAttribute('style', `${contextStyle};${HIDDEN_STYLE}`) ;(hiddenTextarea as HTMLTextAreaElement).value = targetElement.value || targetElement.placeholder || '' let height = hiddenTextarea.scrollHeight const result = {} as TextAreaHeight if (boxSizing === 'border-box') { height = height + borderSize } else if (boxSizing === 'content-box') { height = height - paddingSize } ;(hiddenTextarea as HTMLTextAreaElement).value = '' const singleRowHeight = hiddenTextarea.scrollHeight - paddingSize if (minRows !== null) { let minHeight = singleRowHeight * minRows if (boxSizing === 'border-box') { minHeight = minHeight + paddingSize + borderSize } height = Math.max(minHeight, height) result.minHeight = `${minHeight}px` } if (maxRows !== null) { let maxHeight = singleRowHeight * maxRows if (boxSizing === 'border-box') { maxHeight = maxHeight + paddingSize + borderSize } height = Math.min(maxHeight, height) } result.height = `${height}px` hiddenTextarea.parentNode?.removeChild(hiddenTextarea) hiddenTextarea = null return result }