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Question

Why function dont want write to the demo pragraph for second press button with other value?

 function check(x){ if (x == 0,100) {return 1;} else { return 25;}; } function test2() { var y,input; input = document.getElementById("input2").value; y = check(input); $("#demo2").html( y ); } 

 <script src="https://ajax.googleapis.com/ajax/libs/jquery/2.1.1/jquery.min.js"></script> <input type="number" id="input2"> <button id="but" onclick ="test2()">Try it</button> <p id="demo2"></p> 

Answer 1

It's because your check() function always return 1 and your p is overwritten each time you press the button.

what do you want to achieve in your if() ?

EDIT

Change your if to

if (x != '' && (x == 0 || x == 100))