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@@ -0,0 +1,100 @@
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+let hiddenTextarea;
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+
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+const HIDDEN_STYLE = `
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+ height:0 !important;
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+ visibility:hidden !important;
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+ overflow:hidden !important;
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+ position:absolute !important;
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+ z-index:-1000 !important;
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+ top:0 !important;
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+ right:0 !important
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+`;
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+
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+const CONTEXT_STYLE = [
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+ 'letter-spacing',
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+ 'line-height',
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+ 'padding-top',
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+ 'padding-bottom',
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+ 'font-family',
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+ 'font-weight',
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+ 'font-size',
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+ 'text-rendering',
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+ 'text-transform',
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+ 'width',
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+ 'text-indent',
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+ 'padding-left',
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+ 'padding-right',
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+ 'border-width',
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+ 'box-sizing'
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+];
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+
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+function calculateNodeStyling(node) {
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+ const style = window.getComputedStyle(node);
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+
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+ const boxSizing = style.getPropertyValue('box-sizing');
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+
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+ const paddingSize = (
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+ parseFloat(style.getPropertyValue('padding-bottom')) +
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+ parseFloat(style.getPropertyValue('padding-top'))
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+ );
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+
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+ const borderSize = (
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+ parseFloat(style.getPropertyValue('border-bottom-width')) +
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+ parseFloat(style.getPropertyValue('border-top-width'))
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+ );
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+
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+ const contextStyle = CONTEXT_STYLE
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+ .map(name => `${name}:${style.getPropertyValue(name)}`)
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+ .join(';');
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+
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+ return { contextStyle, paddingSize, borderSize, boxSizing };
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+}
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+
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+export default function calcTextareaHeight(
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+ targetNode,
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+ minRows = null,
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+ maxRows = null
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+) {
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+ if (!hiddenTextarea) {
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+ hiddenTextarea = document.createElement('textarea');
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+ document.body.appendChild(hiddenTextarea);
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+ }
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+
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+ let {
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+ paddingSize,
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+ borderSize,
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+ boxSizing,
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+ contextStyle
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+ } = calculateNodeStyling(targetNode);
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+
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+ hiddenTextarea.setAttribute('style', `${contextStyle};${HIDDEN_STYLE}`);
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+ hiddenTextarea.value = targetNode.value || targetNode.placeholder || '';
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+
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+ let height = hiddenTextarea.scrollHeight;
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+
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+ if (boxSizing === 'border-box') {
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+ height = height + borderSize;
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+ } else if (boxSizing === 'content-box') {
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+ height = height - paddingSize;
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+ }
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+
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+ hiddenTextarea.value = '';
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+ let singleRowHeight = hiddenTextarea.scrollHeight - paddingSize;
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+
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+ if (minRows !== null) {
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+ let minHeight = singleRowHeight * minRows;
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+ if (boxSizing === 'border-box') {
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+ minHeight = minHeight + paddingSize + borderSize;
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+ }
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+ height = Math.max(minHeight, height);
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+ }
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+ if (maxRows !== null) {
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+ let maxHeight = singleRowHeight * maxRows;
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+ if (boxSizing === 'border-box') {
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+ maxHeight = maxHeight + paddingSize + borderSize;
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+ }
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+ height = Math.min(maxHeight, height);
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+ }
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+
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+ return { height: height + 'px'};
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+};
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