<h3>输入完按回车后即可验证！（自认为最简单！）</h3>
正整数: <input type="text" size="20" onkeydown="if(event.keyCode == 13) alert(/^\d+$/.test(this.value));">
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负整数: <input type="text" size="20" onkeydown="if(event.keyCode == 13) alert(/^-\d+$/.test(this.value));">
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整 数: <input type="text" size="20" onkeydown="if(event.keyCode == 13) alert(/^-?\d+$/.test(this.value));">
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正小数: <input type="text" size="20" onkeydown="if(event.keyCode == 13) alert(/^\d+\.\d+$/.test(this.value));">
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负小数: <input type="text" size="20" onkeydown="if(event.keyCode == 13) alert(/^-\d+\.\d+$/.test(this.value));">
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小 数: <input type="text" size="20" onkeydown="if(event.keyCode == 13) alert(/^-?\d+\.\d+$/.test(this.value));">
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实 数: <input type="text" size="20" onkeydown="if(event.keyCode == 13) alert(/^-?\d+\.?\d*$/.test(this.value));">
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保留1位小数:<input type="text" size="20" onkeydown="if(event.keyCode == 13) alert(/^-?\d+\.?\d{0,1}$/.test(this.value));">
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保留2位小数:<input type="text" size="20" onkeydown="if(event.keyCode == 13) alert(/^-?\d+\.?\d{0,2}$/.test(this.value));">
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保留3位小数:<input type="text" size="20" onkeydown="if(event.keyCode == 13) alert(/^-?\d+\.?\d{0,3}$/.test(this.value));">
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