如何从函数内部获取变量？

Question

I'm trying to access myVariable outside this function. Please see the code below:

var myVariable;
function drawBasic(){
...
  myVariable = document.getElementById('chart_div3');
  var chart = new google.visualization.LineChart(document.getElementById('chart_div'));


google.visualization.events.addListener(chart, 'ready', function () {
        chart_div.innerHTML = '<img src="' + chart.getImageURI() + '">';

        myVariable.innerHTML = chart.getImageURI();
        
        myVariable = myVariable.innerHTML;

        //prints out desired value
        console.log(myVariable);


});

//prints out desired value
console.log(myVariable);
...
}
//prints out undefined
    console.log(myVariable);

I know that myVariable is defined outside the function so I was hoping it could be set inside the function and then the value could be used anywhere else, but I was wrong. So my question would be how can I get the value of chart.getImageURI() and store it as a value outside the function drawBasic ?

Answer 1

I think this is because of a issue with your syntax in " var = myVariable ". I wrote this and it works fine.

var myVariable;
drawBasic();
function drawBasic(){
   myVariable = "Test String";
   //prints out desired value
   console.log(myVariable);
}
//prints out undefined
console.log(myVariable);

jsfiddle example

Answer 2

您可以将您的 chart.getImageURI() 放在 window.myVariable （始终可访问）或隐藏表单输入中，在您的函数中使用 jquery ： $("#myHiddenItem").val(chart.getImageURI()) 以及您的位置需要值：$("#myHiddenItem").val()

Answer 3

The reason your result is undefined is probably because of the order in which your code is executed: your last console.log() is called after drawBasic() is defined , but probably before drawBasic() is executed .

Inside the function, you can do:

myVariable = chart.getImageURI();

The value of the global (and therefore readable everywhere) variable myVariable will be set when the function is called.

After you execute drawBasic(), the value of myVariable should be correct, also when called outside the function.