参考这个
<input type="text" name="test" onkeyup="aaa()"></input>
<SCRIPT ID=clientEventHandlersJS LANGUAGE=javascript>
function aaa() {
if (test.value.length==4){
test.value= test.value+"-"
}
if (test.value.length==7){
test.value= test.value+"-"
}
}
</script>
<input type="text" name="test" onkeyup="aaa()"></input>
<SCRIPT ID=clientEventHandlersJS LANGUAGE=javascript>
function aaa() {
if (test.value.length==4){
test.value= test.value+"-"
}
if (test.value.length==7){
test.value= test.value+"-"
}
}
</script>
像seltext
var range = document.body.createTextRange();
range.moveToElementText(demo)
range.findText(str);
range.select();
}