How to clear the default value of input

<Input name = "username" type = "text" value = "first name. last name "size =" 15 "maxlength =" 60 "onfocus =" this. value = ''">
What should I do if I move the mouse away and have the default value?
<Input name = "username" type = "text" value = "first name. last name "size =" 15 "maxlength =" 60 "onfocus =" value = ''" onblur = "if (! Value) value = defaultValue ">
[Ctrl + A select all Note: If you need to introduce external Js, You need to refresh it to execute]

It seems that there are still some problems. When I input it, moving the mouse away will not be restored to the original default value, but if I want to modify my input, it will not work. click the mouse and the input is cleared again.
<Input type = "text" onblur = "showSearch (this, 1)" onfocus = "showSearch (this)" name = "KeyWord" value = "Enter keywords for search"/>
[Ctrl + A select all Note: If you need to introduce external Js, You need to refresh it to execute]
And the moderator only needs to change:
<Input name = "username" type = "text" value = "first name. last name "size =" 15 "maxlength =" 60 "onfocus =" if (value = defaultValue) value = ''" onblur = "if (! Value) value = defaultValue ">
[Ctrl + A select all Note: If you need to introduce external Js, You need to refresh it to execute]