Javascript 预设文字 单击消失

var state = 1;

function transfer1To2() {
    if(state == 1) {
        document.getElementById('textbox').value = "";
        state = 2;
    }
}

function transfer2To3() {
    if(state == 2) {
        state = 3;
    }
}

function transfer2To1() {
    if(state == 2) {
        document.getElementById('textbox').value = "預設文字";
        state = 1;
    }
}

<input name="textbox" id="textbox" type="text" value="預設文字"
    onMouseDown="transfer1To2();"
    onFocus="transfer1To2();"
    onChange="transfer2To3();"
    onBlur="transfer2To1();">