<!DOCTYPE html> <html> <head> <title> TEST </title> <meta charset="utf8"> </head> <body> <input type="text" name="text" value=" " placeholder="1" onkeyup="verif(this);"/> <script type="text/javascript"> function verif(elm) { var valElm = elm.value; var firstChar = valElm.length>1 ? valElm.charAt(0) : valElm; if(firstChar < 1){ elm.value = ""; } return true; } </script> </body> </html>