javascript - Get an element of an array only once -

i have array 4 colors.

ex:

var c1 = getcolor(); var c2 = getcolor(); var c3 = getcolor(); var c4 = getcolor();  function geracolor() {     var colors = ['#3498db', '#8e44ad', '#e67e22', '#1abc9c'];     //return each value once } 

i have list of teachers, each teacher has sublist disciplines.
this: professor , disciplines

each time click on professor, everytime click on professor's name, add disciplines inside calendar (alreay done).

what need is: need generate unique color (random or not) each professor click/expand.

obs: have limit of 4 professors, need generate 4 colors.
obs2: everytime click again on professor, closing disciplines. need make color using avaliable again.

afa understood question, maybe want achieve :

var colors = ["red", "green", "yellow", "orange", "blue", "pink"];  var defaultcolor = "black";    function getrndcolor() {    var size = colors.length;    var rnd = math.floor(math.random() * size);    return colors.splice(rnd, 1)[0];  }    function getcolor(elem) {    var color = defaultcolor;    if (elem.checked) {      color = getrndcolor();    } else {      colors.push(elem.parentelement.style.color);    }    elem.parentelement.style.color = color;    console.log(colors);  }

<span><input type="checkbox" onclick="getcolor(this)"/>get random color</span>    <span><input type="checkbox" onclick="getcolor(this)"/>get random color</span>  <br/>  <span><input type="checkbox" onclick="getcolor(this)"/>get random color</span>    <span><input type="checkbox" onclick="getcolor(this)"/>get random color</span>  <br/>