通过onclick传递变量

function $id(id) {
    return document.getElementById(id);
}

/*
    internal representation
    these values changed only by the gotoPage function
    invariant:
        - rightPage is always equal to leftPage+1
        - iframes always show leftPage.jpg and rightPage.jpg, 
          except if it\'s an invalid page, in which case that 
          iframe shows an about:blank
*/
var leftPage = 0; // page0 is blank
var rightPage = 1; // must always be equal to leftPage+1; which may be an invalid page
var PAGE_MAX = ???;
function gotoPage(num) {
    if (num<0)
        num = 0;
    if (num>PAGE_MAX)
        num = PAGE_MAX; // may need to think about this some more

    // most books seem to put even pages on left and odd on right
    function isEven(n) {
        return n%2==0; // sidenote: abs(n%2)==1 -> odd
    }
    leftPage = isEven(num) ? num : num-1;
    rightPage = leftPage+1;

    updateDisplay();
}

function prev() {
    gotoPage(leftPage-2);
}
function next() {
    gotoPage(leftPage+2);
}
function gotoPageByGuess(elem) {
    var pageNum = parseInt(elem.innerHTML.slice(-2));
    gotoPage(pageNum);
}

function updateDisplay() {
    // using jquery
    $id(\'leftPage\').src = \'page\'+leftPage+\'.jpg\';
    if (rightPage <= PAGE_MAX)
        $id(\'rightPage\').src = \'page\'+rightPage+\'.jpg\';
    else
        $id(\'rightPage\').src = \'about:blank\';            
}

<a onclick=\"prev()\">Previous</a>
<a onclick=\"next()\">Next</a>

<a onclick=\"gotoPage(26)\">Chapter 2: Some Title......... p26</a>
<a onclick=\"gotoPageByGuess(this)\">Chapter 2: Some Title......... p26</a>