<input onkeydown="return event.keyCode>=48&&event.keyCode<=57||event.keyCode>=96&&event.keyCode<=105" />

function validateDigitsOnly(evt) {
var e = evt || window.event,
key = e.keyCode || e.which;
if (
// Backspace, Tab, Enter, Esc, Delete
key == 8 || key == 9 || key == 13 || key == 27 || key == 46 ||
// Ctrl + A
(key == 65 && event.ctrlKey === true) ||
// Home, End, 四個(gè)方向鍵
key >= 35 && key <= 40) {
return;
}
if (e.shiftKey || e.altKey || e.ctrlKey) {
return false;
}
var el = e.target || e.srcElement,
// 最大數(shù)字長(zhǎng)度
nl = el.getAttribute("data-numbers") || 15,
// 最大小數(shù)長(zhǎng)度
dl = el.getAttribute("data-decimals") || 2,
val = el.value,
// "." 位置
dotIndex = val.indexOf("."),
rng = caret.call(el),
// 光標(biāo)在"."左邊
rLeft = rng.end <= dotIndex,
// 光標(biāo)在"."右邊
rRight = rng.begin > dotIndex;
if (
// 數(shù)字
key >= 48 && key <= 57 ||
// 數(shù)字鍵盤(pán)輸入的數(shù)字
key >= 96 && key <= 105) {
if (validateValue(dotIndex, val, rLeft, rRight, nl, dl))
return;
// 選中部分文本再做一次處理
val = val.substring(0, rng.begin) + val.substring(rng.end);
dotIndex = val.indexOf(".");
if (validateValue(dotIndex, val, rLeft, rRight, nl, dl))
return;
}
else if (
// ".", ","
(key == 190 /*|| key == 188*/ ||
// 數(shù)字鍵盤(pán)上的 ".", ","
key == 110/*|| key == 109*/) &&
// 允許輸入小數(shù)
dl > 0) {
if (
// 未輸入".", 且輸入的位置后面的小數(shù)位數(shù)未達(dá)到上限
dotIndex == -1 && (rng.end == val.length || val.substring(rng.end).length <= dl) ||
// 輸過(guò)".", 且選中部分文本包含"."
dotIndex > -1 && rng.begin <= dotIndex && dotIndex < rng.end)
return;
}
return false;
}
// 驗(yàn)證輸入的值
function validateValue(dotIndex, val, rLeft, rRight, nl, dl) {
if (
// 未輸入過(guò)"."
dotIndex == -1 && val.length < nl ||
// 光標(biāo)位置在"."之前
rLeft && val.substring(0, dotIndex).length < nl ||
// 光標(biāo)在"."之后且未達(dá)到小數(shù)上限
rRight && val.substring(dotIndex + 1).length < dl)
return true;
return false;
}
// 獲取光標(biāo)位置
function caret() {
var begin, end;
if (this.setSelectionRange) {
begin = this.selectionStart;
end = this.selectionEnd;
} else if (document.selection && document.selection.createRange) {
var range = document.selection.createRange();
begin = 0 - range.duplicate().moveStart('character', -100000);
end = begin + range.text.length;
}
return { begin: begin, end: end };
}

<input type="text" id="t1" />
<input type="text" id="t2" data-numbers="5" data-decimals="4" />
<script>
document.getElementById("t1").onkeydown = validateDigitsOnly;
document.getElementById("t2").onkeydown = validateDigitsOnly;
</script>

<input type="text" id="lwme_text_3" onkeydown="return validateDigitsOnly(event)" />

<input type="text" class="digitsOnly" />

$(".digitsOnly").keydown(validateDigitsOnly);