使用javascript开发超棒的动画文字书写效果

  <div id="letter"></div>
    <img id="inkwell1" src="inkwell1.gif" alt="inkwell1" />
    <img id="inkwell2" src="inkwell2.gif" alt="inkwell2" />
 
    <div id="letter_src">
A man named Grant once foi|und a box of old Papers in his dwelling||||||||house. Grant didn't like old things. So he burned most of the papers. But one of these papers was a letter. He read it. A well-known writer had written it.<br><br>
'About a million|||||||hundred years ago nobody know about him|||this writer,' thought Grant. 'Nobody read his books. But now everybody reads him. Some people like to buy old letters. I can get a lot of money for this letter.'<br><br>
But the letter looked dirty. So Grant decided to wash |||||clean it. He worked hard and soon the letter looked new. Grant was not|||||||was very happy.<br><br>
He took the letter to a shop in London where they bought and sold old papers. 'I want to sell this letter,' Grant said to the man in shop. 'It is a well-known writer's letter. How much will you give me for it?'<br><br>
The man looked at the letter for a long time. 'I'll give you two pounds for it,' he said at last.<br><br>
'Only two pounds!' said Grant. 'But people pay ten pounds for old letters. And I have even cleaned it.'<br><br>
'I can see that,' said the man. 'That's the mistake. People who buy old papers like dirty papers more than clean papers.'<br><br>
    </div>

 window.onload = function(){
    // public variables
    var vLetter = document.getElementById('letter');
    var iSpeedInk = 5;
 
    // other variables
    var sText = document.getElementById('letter_src').innerHTML;
    var iCurChar = 0;
    var sChars = '<span>';
    var iCurInk = 0;
    var sCurCaret = '';
    var sCaret = " <img src="pen.gif" style='position:absolute' />";
 
    var doStep = function () {
        // current char
        var sChar = sText.charAt(iCurChar);
 
        // default char delay
        var iDelay = 32;
 
        if (sChar == '') {
            sCurCaret = '';
        } else if (sChar == '|') { // we use | symbol to emulate 'error' symbol
            sChar = '';
            sChars = sChars.substring(0, sChars.length-1);
            iDelay = 64;
        } else if (sChar == '<') { // pass tags
            var iPos = sText.indexOf('>', iCurChar);
            sChar = sText.substring(iCurChar, iPos + 1);
            iCurChar = iPos;
        } else if (sChar == '&') { // pass html entities
            var iPos = sText.indexOf(';', iCurChar);
            sChar = sText.substring(iCurChar, iPos + 1);
            iCurChar = iPos;
        } else if (sChar == '.') { // custom delay in case of . symbol
            iDelay = 300;
        } else if (sChar == ',') { // custom delay in case of , symbol
            iDelay = 100;
        } else if (sChar == ' ') { // custom delay in case of space symbol
            iDelay = 32;
        } else if (iCurChar > 5) {
            sCurCaret = sCaret;
        }
 
        // expenditure of ink
        if (sChar == ' ') {
            iCurInk += iSpeedInk;
            sChar = '</span><span style="color:RGB(' + (iCurInk) + ',' + (iCurInk) + ',' + (iCurInk) + ')">' + sChar;
        }
 
        if (document.getElementById('inkwell2').style.visibility == 'visible') {
            sCurCaret = sCaret;
            document.getElementById('inkwell2').style.visibility = 'hidden';
            sChar = '</span><span style="color:RGB(0,0,0)">' + sChar;
        }
 
        // refresh Ink
        if (iCurInk > 160) {
            iCurInk = 0;
            document.getElementById('inkwell2').style.visibility = 'visible';
            iDelay = 1000;
            sCurCaret = '';
        }
 
        // add current char to chars
        sChars += sChar;
 
        // hide the caret at the end of the letter
        if (iCurChar == sText.length - 1)
            sCurCaret = '';
 
        // update letter with new chars
        vLetter.innerHTML = sChars + sCurCaret;
 
        // goto next char
        iCurChar++;
 
        // next step
        if (iCurChar < sText.length) {
            setTimeout(doStep, 20 + iDelay);
        }
    }
 
    doStep();
};