Default text on input

In modern browsers, you may set the placeholder attribute on a field to set its default text.

<input type="text" placeholder="Type some text" id="myField" />

However, in older browsers, you may use JavaScript to capture the focus and blur events:

var addEvent = function(elem, type, fn) { // Simple utility for cross-browser event handling
    if (elem.addEventListener) elem.addEventListener(type, fn, false);
    else if (elem.attachEvent) elem.attachEvent('on' + type, fn);
},
textField = document.getElementById('myField'),
placeholder = 'Type some text'; // The placeholder text

addEvent(textField, 'focus', function() {
    if (this.value === placeholder) this.value = '';
});
addEvent(textField, 'blur', function() {
    if (this.value === '') this.value = placeholder;
});

Demo: http://jsbin.com/utecu