如何在JavaScript中的按键事件上获取文本框的值

Question

I am making a chrome extension in which I want to do some string replacement in the text when the enter key is pressed in a focussed textarea. Here is the code snippet:

var elems = document.getElementById("ChatTabsPagelet").getElementsByTagName("textarea"),i;
matchClass = "uiTextareaAutogrow";

for (i in elems) {
    if((' ' + elems[i].className + ' ').indexOf(' ' + matchClass + ' ')> -1) {
    text = elems[i].value;          
            elems[i].onkeyup = function(evt) {
              if(evt.keyCode == 13){
               alert(elems[i].value);
              }
      };
   }
}

Basically I am looking for all the textareas with the class uiTextareaAutogrow and I just want to access their values when the enter key is pressed in any of those textareas. However, I always get undefined in the alert box when I try the extension out on a webpage. I guess the keyup event is fired but it is not able to get a handle to the particular textarea. Where am I going wrong?

Note: I am keen on using javascript only(not jquery) as I want the extension to be really light.

Answer 1

The following example should do the trick! ( see a working JSFiddle here ).

You shouldn't use for..in with array-like objects as the order cannot be guaranteed. Also when the value of an element is referenced in a dynamic function you need to use this.value .

var elems = document.getElementsByTagName("textarea")
matchClass = "uiTextareaAutogrow";
for(var i = 0, n = elems.length; i < n; i++) { // <---- simple for loop
    if((' ' + elems[i].className + ' ').indexOf(' ' + matchClass + ' ')> -1) {
             elems[i].onkeyup = function(evt) {
                  if(evt.keyCode == 13){
                      alert(this.value);
                   }
            }  
    }
}