Question

67

Problem keeping variable alive in a javascript function

rated 0 times [ 69] [ 2] / answers: 1 / hits: 30234 / 12 Years ago, fri, may 4, 2012, 12:00:00

I want to house a variable in a function. This variable will change state depending on user interaction. For example:

function plan_state(current){

    if (current != ''){

        state = current;

    }

    else {

        return state;

    }

}

When the document loads I call plan_state('me'), and when certain things happen I may call plan_state('loved'). The problem occurs when I run a function and want to check the current state:

alert(plan_state());

I get undefined back, but the value should be 'me' as I previously set this value on document load.

What am I doing wrong?

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answered 12 Years ago carolyn · Accepted Answer

The function isn't stateful because the state variable is declared inside the function and therefore only exists for the lifetime of the function call. An easy solution would be to declare the variable globally, outside the function. This is bad bad bad bad.

A better approach is to use the module pattern. This is an essential pattern to learn if you're serious about javascript development. It enables state by means of internal (private variables) and exposes a number of methods or functions for changing or getting the state (like object oriented programming)

    var stateModule = (function () {

        var state; // Private Variable



        var pub = {};// public object - returned at end of module



        pub.changeState = function (newstate) {

            state = newstate;

        };



        pub.getState = function() {

            return state;

        }



        return pub; // expose externally

    }());

so stateModule.changeState(newstate); sets the state

and var theState = stateModule.getState(); gets the state