function one(){
    ...../*code*/
    ........
    ../*somewhere in this function i have*/

    var t = document.createElementNS('http://www.w3.org/2000/svg','text');
            t.setAttribute("id", "textError");
            t.textContent = ("hello")
            svgError.appendChild(t);

    }

function second() {
    one();
}

function second() {
    one();
    document.querySelector("#textError").textContent = ("new text");
}

function one(textContent){
    ....................
    ....................
    var t = document.createElementNS('http://www.w3.org/2000/svg','text');
    t.setAttribute("id", "textError");
    t.textContent = textContent?textContent:"hello";
    svgError.appendChild(t);
    ....................
    ....................
}

function second() {
    one("new text");
}

function second() {
    var newText = this.getText();
    one(newText); // one(this.getText());
}