javascript - 如何从所选文本中获取相邻字符？

Question

我有这样一个字符串:

var comment = 'this is a test';

假设选择了this i，现在我需要null(左侧)和s(右侧)。我怎样才能得到它们？

---

我可以获得这样的选定文本:

function getSelectionHtml() {
    var html = "";
    if (typeof window.getSelection != "undefined") {
        var sel = window.getSelection();
        if (sel.rangeCount) {
            var container = document.createElement("div");
            for (var i = 0, len = sel.rangeCount; i < len; ++i) {
                container.appendChild(sel.getRangeAt(i).cloneContents());
            }
            html = container.innerHTML;
        }
    } else if (typeof document.selection != "undefined") {
        if (document.selection.type == "Text") {
            html = document.selection.createRange().htmlText;
        }
    }
    return html;
}

var selected_text = getSelectionHtml();

Answer 1

document.addEventListener("click", function() {
  var selection = window.getSelection();
  // Check if there are any ranges selected.
  if (selection.rangeCount > 0 && selection.type == "Range") {
    // Text content of the element.
    var text = selection.anchorNode.textContent;
    // selection.anchorOffset is the start position of the selection
    var before = text.substring(selection.anchorOffset-1, selection.anchorOffset);
    // selection.extentOffset is the end position of the selection
    var after = text.substring(selection.extentOffset, selection.extentOffset+1);
    // Check if there are any letters before or after selected string.
    // If not, change before and after to null.
    before = before.length === 1 ? before : null;
    after = after.length === 1 ? after : null;
    console.log(before, after);
  }
});

<div>this is a test</div>

获取两个字符:

document.addEventListener("click", function() {
  var selection = window.getSelection();
  // Check if there are any ranges selected.
  if (selection.rangeCount > 0 && selection.type == "Range") {
    // Text content of the element.
    var text = selection.anchorNode.textContent;
    // selection.anchorOffset is the start position of the selection
    var before = text.substring(selection.anchorOffset-2, selection.anchorOffset);
    // selection.extentOffset is the end position of the selection
    var after = text.substring(selection.extentOffset, selection.extentOffset+2);
    // Check if there are any letters before or after selected string.
    // If not, change before and after to null.
    before = before.length >= 1 ? before : null;
    after = after.length >= 1 ? after : null;
    console.log(before, after);
  }
});

<div>this is a test</div>