userscripts - Obtain and check the value of an input text with javascript -


i new javascript , need script obtain value of input text , check value if equal 0 (zero). if need alert message notifying me text input 0. thanks.

<input id="txtval" type="text" name="txtval" value="0" maxlength="10">

the short answer:

if(txval.value==0) alert('please enter number.');

is not best answer:

var v=document.getelementbyid('txtval'); v=parseint(v,10); if(v<=0) alert('please enter positive integer.');

of course not best answer either fix couple of common mistakes.

  • although can refer element using id variable name not recomended.
  • the value property of input (ie txtval.value) string (even if contains digits) if try compare number may unexpected results. in case comparing 0 problems less if ever change code compare number run problems, best make actual number before it.

if want allow decimals use parsefloat instead.


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