var fn = window[settings.functionName];
if(typeof fn === ‘function’) {
fn(t.parentNode.id);
}

编辑：
在这种情况下，settings.functionName将是"clickedOnItem"。这将在运行时转换varfn=window[settings.functionName];为var fn =window["clickedOnItem"]，从而获得对的引用function clickedOnItem (nodeId) {}。一旦引用了变量内的函数，就可以通过“调用变量”来调用该函数，即fn(t.parentNode.id)，等于clickedOnItem(t.parentNode.id)OP所需要的。

更完整的例子：

/* Somewhere: */
window.settings = {
  /* [..] Other settings */
  functionName: 'clickedOnItem'
  /* , [..] More settings */
};

/* Later */
function clickedOnItem (nodeId) {
  /* Some cool event handling code here */
}

/* Even later */
var fn = window[settings.functionName]; 
/* note that settings.functionName could also be written
   as window.settings.functionName. In this case, we use the fact that window
   is the implied scope of global variables. */
if(typeof fn === 'function') {
    fn(t.parentNode.id);
}