You can't use characters in an HTML attribute value which doesn't have delimiters and you are missing a ).

You could add the missing bits:

sb.append(<a href='javascript:testFunction(+str+);'>test</a>);

But you would be better off:

• Not constructing JavaScript by mashing together strings


• Not constructing HTML by mashing together strings


• Not using a link to run JavaScript

Such:

var button = document.createElement('button');

button.type = button;

button.appendChild(

    document.createTextNode('test')

);

button.addEventListener('click', function (event) {

    testFunction(str);

});

ab.append(button); // Assuming that whatever `ab.append` is accepts a DOM element