javascript获取以及设置光标位置

// 获取光标位置
function getCursortPosition (textDom) {
    var cursorPos = 0;
    if (document.selection) {
        // IE Support
        textDom.focus ();
        var selectRange = document.selection.createRange();
        selectRange.moveStart (‘character‘, -textDom.value.length);
        cursorPos = selectRange.text.length;
    }else if (textDom.selectionStart || textDom.selectionStart == ‘0‘) {
        // Firefox support
        cursorPos = textDom.selectionStart;
    }
    return cursorPos;
}

// 设置光标位置
function setCaretPosition(textDom, pos){
    if(textDom.setSelectionRange) {
        // IE Support
        textDom.focus();
        textDom.setSelectionRange(pos, pos);
    }else if (textDom.createTextRange) {
        // Firefox support
        var range = textDom.createTextRange();
        range.collapse(true);
        range.moveEnd(‘character‘, pos);
        range.moveStart(‘character‘, pos);
        range.select();
    }
}

// 获取选中文字
function getSelectText() {
    var userSelection, text;
    if (window.getSelection) {
        // Firefox support
        userSelection = window.getSelection();
    } else if (document.selection) {
        // IE Support
        userSelection = document.selection.createRange();
    }
    if (!(text = userSelection.text)) {
        text = userSelection;
    }
    return text;
}

/**
* 选中特定范围的文本
* 参数：
*     textDom  [JavaScript DOM String] 当前对象
*     startPos  [Int]  起始位置
*     endPos  [Int]  终点位置
*/
function setSelectText(textDom, startPos, endPos) {
    var startPos = parseInt(startPos),
        endPos = parseInt(endPos),
        textLength = textDom.value.length;
    if(textLength){
        if(!startPos){
            startPos = 0;
        }
        if(!endPos){
            endPos = textLength;
        }
        if(startPos > textLength){
            startPos = textLength;
        }
        if(endPos > textLength){
            endPos = textLength;
        }
        if(startPos < 0){
            startPos = textLength + startPos;
        }
        if(endPos < 0){
            endPos = textLength + endPos;
        }
        if(textDom.createTextRange){
            // IE Support
            var range = textDom.createTextRange();
            range.moveStart("character",-textLength);
            range.moveEnd("character",-textLength);
            range.moveStart("character", startPos);
            range.moveEnd("character",endPos);
            range.select();
        }else{
            // Firefox support
            textDom.setSelectionRange(startPos, endPos);
            textDom.focus();
        }
    }
}

/**
* 在光标后插入文本
* 参数：
*     textDom  [JavaScript DOM String] 当前对象
*     value  [String]  要插入的文本
*/
function insertAfterText(textDom, value) {
    var selectRange;
    if (document.selection) {
        // IE Support
        textDom.focus();
        selectRange = document.selection.createRange();
        selectRange.text = value;
        textDom.focus();
    }else if (textDom.selectionStart || textDom.selectionStart == ‘0‘) {
        // Firefox support
        var startPos = textDom.selectionStart;
        var endPos = textDom.selectionEnd;
        var scrollTop = textDom.scrollTop;
        textDom.value = textDom.value.substring(0, startPos) + value + textDom.value.substring(endPos, textDom.value.length);
        textDom.focus();
        textDom.selectionStart = startPos + value.length;
        textDom.selectionEnd = startPos + value.length;
        textDom.scrollTop = scrollTop;
    }
    else {
        textDom.value += value;
        textDom.focus();
    }
}