zent/src/utils/dom/getCaretCoordinates.ts

一套前端设计语言和基于React的实现

/* Modified from https://github.com/component/textarea-caret-position/blob/master/index.js */

import createElement from './createElement';
import isBrowser from '../isBrowser';
import isFirefox from '../isFirefox';

// We'll copy the properties below into the mirror div.
// Note that some browsers, such as Firefox, do not concatenate properties
// into their shorthand (e.g. padding-top, padding-bottom etc. -> padding),
// so we have to list every single property explicitly.
const properties = [
  'direction', // RTL support
  'boxSizing',
  'width', // on Chrome and IE, exclude the scrollbar, so the mirror div wraps exactly as the textarea does
  'height',
  'overflowX',
  'overflowY', // copy the scrollbar for IE

  'borderTopWidth',
  'borderRightWidth',
  'borderBottomWidth',
  'borderLeftWidth',
  'borderStyle',

  'paddingTop',
  'paddingRight',
  'paddingBottom',
  'paddingLeft',

  // https://developer.mozilla.org/en-US/docs/Web/CSS/font
  'fontStyle',
  'fontVariant',
  'fontWeight',
  'fontStretch',
  'fontSize',
  'fontSizeAdjust',
  'lineHeight',
  'fontFamily',

  'textAlign',
  'textTransform',
  'textIndent',
  'textDecoration', // might not make a difference, but better be safe

  'letterSpacing',
  'wordSpacing',

  'tabSize',
  'MozTabSize',
];

const MIRROR_DIV_ID = 'zent-input-textarea-caret-coordinates-mirror-div';

export interface IGetCaretCoordinatesOption {
  debug?: boolean;
}

function getCaretCoordinates(
  element: HTMLInputElement | HTMLTextAreaElement,
  position: number,
  { debug }: IGetCaretCoordinatesOption
) {
  if (!isBrowser) {
    throw new Error('getCaretCoordinates should only be called in a browser');
  }

  if (debug) {
    const el = document.getElementById(MIRROR_DIV_ID);
    if (el) el.parentNode.removeChild(el);
  }

  // The mirror div will replicate the textarea's style
  const div = createElement('div');
  div.id = MIRROR_DIV_ID;
  document.body.appendChild(div);

  const style = div.style;
  const computed = getComputedStyle(element);
  const isInput = element.nodeName === 'INPUT';

  // Default textarea styles
  if (!isInput) {
    style.whiteSpace = 'pre-wrap';
    style.wordWrap = 'break-word'; // only for textarea-s
  } else {
    style.whiteSpace = 'nowrap';
  }

  // Position off-screen
  style.position = 'absolute'; // required to return coordinates properly
  if (!debug) style.visibility = 'hidden'; // not 'display: none' because we want rendering

  // Transfer the element's properties to the div
  properties.forEach(prop => {
    if (isInput && prop === 'lineHeight') {
      // Special case for <input>s because text is rendered centered and line height may be != height
      style.lineHeight = computed.height;
    } else {
      style[prop] = computed[prop];
    }
  });

  if (isFirefox) {
    // Firefox lies about the overflow property for textareas: https://bugzilla.mozilla.org/show_bug.cgi?id=984275
    if (element.scrollHeight > parseInt(computed.height, 10)) {
      style.overflowY = 'scroll';
    }
  } else {
    style.overflow = 'hidden'; // for Chrome to not render a scrollbar; IE keeps overflowY = 'scroll'
  }

  div.textContent = element.value.substring(0, position);
  // The second special handling for input type="text" vs textarea:
  // spaces need to be replaced with non-breaking spaces - http://stackoverflow.com/a/13402035/1269037
  if (isInput) div.textContent = div.textContent.replace(/\s/g, '\u00a0');

  const span = createElement('span');
  // Wrapping must be replicated *exactly*, including when a long word gets
  // onto the next line, with whitespace at the end of the line before (#7).
  // The  *only* reliable way to do that is to copy the *entire* rest of the
  // textarea's content into the <span> created at the caret position.
  // For inputs, just '.' would be enough, but no need to bother.
  span.textContent = element.value.substring(position) || '.'; // || because a completely empty faux span doesn't render at all
  div.appendChild(span);

  const rawOffsetLeft =
    span.offsetLeft + parseInt(computed.borderLeftWidth, 10);
  const lineHeight = parseInt(computed.lineHeight, 10);
  const coordinates = {
    top: span.offsetTop + parseInt(computed.borderTopWidth, 10),
    left: rawOffsetLeft,

    // Chrome returns `normal` if you set line-height to `normal`
    // In this case, we use font-size as a fallback
    // The ratio is just a guess
    height: Number.isNaN(lineHeight)
      ? parseInt(computed.fontSize, 10) * 1.5
      : lineHeight,
  };

  if (debug) {
    span.style.backgroundColor = '#aaa';
  } else {
    document.body.removeChild(div);
  }

  return coordinates;
}

export default getCaretCoordinates;