Positive integers: <input type= "text" size= "onkeydown=" if (Event.keycode = =) Alert (/^\d+$/.test (This.value)); " >
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Negative integers: <input type= "text" size= "onkeydown=" if (Event.keycode = =) Alert (/^-\d+$/.test (This.value)); " >
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Integer: <input type= "text" size= "onkeydown=" if (Event.keycode = =) Alert (/^-?\d+$/.test (This.value)); " >
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Positive decimals: <input type= "text" size= "onkeydown=" if (Event.keycode = =) Alert (/^\d+\.\d+$/.test (This.value)); " >
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Negative decimals: <input type= "text" size= "onkeydown=" if (Event.keycode = =) Alert (/^-\d+\.\d+$/.test (This.value)); " >
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Decimals: <input type= "text" size= "onkeydown=" if (Event.keycode = =) Alert (/^-?\d+\.\d+$/.test (This.value)); " >
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Real numbers: <input type= "text" size= "onkeydown=" if (Event.keycode = =) alert (/^-?\d+\.? \d*$/.test (This.value)); " >
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Keep 1 decimal places: <input type= "text" size= "onkeydown=" if (Event.keycode = =) alert (/^-?\d+\.? \d{0,1}$/.test (This.value)); " >
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Keep 2 decimal places: <input type= "text" size= "onkeydown=" if (Event.keycode = =) alert (/^-?\d+\.? \d{0,2}$/.test (This.value)); " >
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Keep 3 decimal places: <input type= "text" size= "onkeydown=" if (Event.keycode = =) alert (/^-?\d+\.? \d{0,3}$/.test (This.value)); " >
JS Regular validation of two decimal places, verifying the simplest regular expression of numbers