Question

How to do this Simple Calculation using JavaScript ? Because i am a beginner.

i want to calculate the value in the same input field.

e.g In the input field, I type the value such as ” 3+4*2 “, then i click the button, the same input field will show the result like “11”.

Here is my code, but not work.

my input type = “text” and id =”expr”

my button type = “button” , value = “Calculate”, onclick = “getAnswer();”

Here is my javascript code.

function getAnswer(){

    val = eval(document.expr.value);
    document.expr.value = val; 

}

but i’m not work.

Answer 1

document.expr most likely does not exist.

Give your input tag an id and use document.getElementById('blah') instead or use document.forms.FORMNAME.expr if the field is inside a form.

Demo: http://jsfiddle.net/ThiefMaster/kRdJH/