Can't do action with node (span)

[Alcadur]

In test case (karma + jasmine) I create input and span:

inputName = document.createElement('input');
inputName.setAttribute('name', 'name');
inputName.value = NAME;

masteredSpan = document.createElement('span');
masteredSpan.className = 'mastered';
masteredSpan.appendChild(document.createTextNode(MASTERED));

One of my test check is masteredSpan changed:

const NEW = 'new mastered';
member.node = document.createElement('li');
member.node.appendChild(inputName);
member.node.appendChild(masteredSpan);

member.update({mastered: NEW});

expect(masteredSpan.textContent).toEqual(NEW);

Member.update fragment:

if(this.node){
    this.node.querySelector('.mastered').textContent = this.mastered || this.masteredDefaultValue;
}

But then I got error: TypeError: Attempted to assign to readonly property.

This error appears even when I try to read any this.node.querySelector('.mastered') property.

NOTE: I use babel

[Alcadur]

I found bug in my configuration file, so there is no bug :)