[monolithed]

На вскидку:

<script>
window.onload = function() {
    var input = document.getElementById('input'), 
        array = ['focus', 'blur'],
        i = array.length;

    while(i--) {
        input['on'+array[i]] = function() {
            var _default = this.defaultValue;
            this.value = this.value == _default ? '' : this.value || _default;  
        };    
    }

};
</script>

<input type="text" value="text" id="input" />