Function insertTextAtPosition

core/src/utils/InsertTextAtPosition.ts:30–124

(input: HTMLTextAreaElement | HTMLInputElement, text: string)

 * @returns {void}
 */
export function insertTextAtPosition(input: HTMLTextAreaElement | HTMLInputElement, text: string): void {
  // Most of the used APIs only work with the field selected
  input.focus();

  // IE 8-10
  if ((document as any).selection) {
    const ieRange = (document as any).selection.createRange();
    ieRange.text = text;

    // Move cursor after the inserted text
    ieRange.collapse(false /* to the end */);
    ieRange.select();

    return;
  }

  // Webkit + Edge
  let isSuccess = false;
  if (text !== '') {
    isSuccess = document.execCommand && document.execCommand('insertText', false, text);
  } else {
    isSuccess = document.execCommand && document.execCommand('delete', false);
  }

  if (!isSuccess) {
    const start = input.selectionStart!;
    const end = input.selectionEnd!;
    // Firefox (non-standard method)
    if (typeof input.setRangeText === 'function') {
      input.setRangeText(text);
    } else {
      // To make a change we just need a Range, not a Selection
      const range = document.createRange();
      const textNode = document.createTextNode(text);

      if (canManipulateViaTextNodes(input)) {
        let node = input.firstChild;

        // If textarea is empty, just insert the text
        if (!node) {
          input.appendChild(textNode);
        } else {
          // Otherwise we need to find a nodes for start and end
          let offset = 0;
          let startNode = null;
          let endNode = null;

          while (node && (startNode === null || endNode === null)) {
            const nodeLength = node.nodeValue!.length;

            // if start of the selection falls into current node
            if (start >= offset && start <= offset + nodeLength) {
              range.setStart((startNode = node), start - offset);
            }

            // if end of the selection falls into current node
            if (end >= offset && end <= offset + nodeLength) {
              range.setEnd((endNode = node), end - offset);