Can I remove 'null' from my drop down selection variable

问题

I have a multi select drop down allowing my user to select multiple A, B and/or C options, using react-select. Each time one is selected, I want it to be added to a 'choice' variable to keep record. I have this working, but since I have to declare my variable first, it is holding 'null' inside the variable. How do I get rid of this? Code below.

handleChange = (selectedChoice) => {
this.setState({ selectedChoice });
for (var i =0; i < selectedChoice.length; i++) {
   var filter = null;
   filter +=(selectedChoice[i].value); //removing the plus just resets it to last chosen option
    }
  console.log(filter);
  }

example of what it prints: nullAC

回答1:

The solution to this was posted in the comments by Yury Tarabanko.

var filter = ''

For good practice console.log would also not be in that position within the code.

来源：https://stackoverflow.com/questions/53263601/can-i-remove-null-from-my-drop-down-selection-variable