JavaScript：当onFocus在此代码中工作时，为什么onKeyDown和onKeyUp不起作用

Question

function PrepareCounter() {
    var ct = 1;
    while(document.getElementById("id_answer"+ct)) {
        document.getElementById("id_answer"+ct).setAttribute("onFocus", "countChars('textbox','char_count',140)", "onKeyDown", "countChars('textbox','char_count',140)", "onKeyUp", "countChars('textbox','char_count',140)");
        ct += 1;
    }
}

If i focus my element countChars is executed but if i write something it's not.

Answer 1

setAttribute only takes 2 arguments, you would have to call each of those separately.

Rather than using strings, you can use real functions:

function PrepareCounter() {
    var ct = 1;
    var elem;
    while (elem = document.getElementById("id_answer" + ct)) {
        elem.onfocus = elem.onkeydown = elem.onkeyup = function() {
            countChars('textbox', 'char_count', 140);
        };
        ct += 1;
    }
}