构造函数中的Javascript函数不适用于onclick

Question

I'm trying to run a function called makeHighlight within my constructor SmartButton. makeHighlight is supposed to run whenever I click on the SmartButton object (an image element) which is why I set the attribute 'onclick' to makeHighlight. I can't get it to work, it either doesn't run at all or runs instantaneously when the page loads.

function SmartButton(buttonId, defaultImage, highlightImage, helpMsg) {
    var newLink = document.createElement('a');
        newLink.setAttribute('href', '#');

    var newImg = document.createElement('img');
        newImg.setAttribute('src', defaultImage);
        newImg.setAttribute('id', buttonId);
        newImg.setAttribute('onclick', "makeHighlight()");

    document.body.appendChild(newLink);
    newLink.appendChild(newImg);

    this.buttonId = buttonId;
    this.defaultImage = defaultImage;
    this.highlightImage = highlightImage;
    this.helpMsg = helpMsg;

    function makeHighlight() {
        newImg.setAttribute('src', highlightImage);
        console.log(this);
    }

}   

button1 = new SmartButton('button1', 'button1off.jpg', 'button1on.jpg', 'sup');

Answer 1

You defined makeHighlight in the scope of SmartButton function. Thus newImg when clicked does not see it. Try this code (inside SmartButton ):

function makeHighlight() {
    newImg.setAttribute('src', highlightImage);
    console.log(this);
}
newImg.onclick = makeHighlight;

(note the lack of brackets in the last line) and remove this line:

newImg.setAttribute('onclick', "makeHighlight()");