javascript - While operator undefined -

i want make small calculator in javascript. got html code looking (for numbers)

<button type="button" onclick="calcnum(1)">1</button> <button type="button" onclick="operator('+')">+</button>   var mynumbers = []; 

the calcnumber function this:

function calcnum(i) {            mynumbers.push(i);     var x = document.getelementbyid("screen").innerhtml = mynumbers.join("");         } 

and operator function this:

function operator(op) {     var operator = op;     var y = document.getelementbyid("screen").innerhtml = operator; } 

my goal make this: if press 1,2,3 want screen element display "123" (which does) if press "+" want "+" displayed (which does) when operator pressed, , new number pressed want start on new number, right if press "123" , + , "456" get:

123456, instead want display "456", hence starting on new number. hope it's clear.

i figured add calcnum function:

while(op == "undefined") {    keep pushing numbers // not work } 

in end want construct calc function takes numbers operator pressed first number, concatanate operator , second number , adding them together.

i see several issues in code don't know if due fact didn't copy code in question.

first, operator function incorrect : give local variable samename function. if want function return value, use returnkeyword.

i figured add calcnum function:

while(op == "undefined") { keep pushing numbers // not work }

where opdefined? op see local variable of operatorfunction. undefined in calcnum.

note if want test if variable undefined, should not test

if (myvar == "undefined") 

but

if(typeof myvar == "undefined") 

finally i'd change code way (should tested though):

var currentnumber= ""; var entries = [] function calcnum(i) {            currentnumber +=i;     document.getelementbyid("screen").innerhtml = currentnumber;        }   function operator(op) {     var y = document.getelementbyid("screen").innerhtml = op;     //note process entered operations if clicked on '='      //and display result instead of displaying operation...     if(currentnumber != ""){//there must number entered before click on operator         entries .push(currentnumber);         entries .push(op);         currentnumber= "";      } } 

and still need of course implement when click on =...