js input 只能输入数字

HTML网页上这么写

<input type="text" style="ime-mode:disabled;" onpaste="return false;" onkeypress="keyPress()" />

function keyPress() {
var keycode = event.keyCode;
if ((keycode >= 48) && (keycode <= 57)) {
event.returnValue = true;
} else {
event.returnValue = false;
}
};