js 光标的位置

function getCursorPosition(input) {
    if ('selectionStart' in input) {
        return input.selectionStart;
    } else if (document.selection) {
        input.focus();
        var range = document.selection.createRange();
        var range_all = document.body.createTextRange();
        range_all.moveToElementText(input);
        for (range_all.moveStart('character', -input.value.length); range_all.compareEndPoints("StartToStart", range) < 0; range_all.moveStart('character', -1)) {
            var start = range_all.text.length;
        }
        return start;
    }
    return -1;
}

function setCursorPosition(input, pos) {
    if (input.setSelectionRange) {
        input.focus();
        input.setSelectionRange(pos, pos);
    } else if (input.createTextRange) {
        var range = input.createTextRange();
        range.collapse(true);
        range.moveEnd('character', pos);
        range.moveStart('character', pos);
        range.select();
    }
}