Multiple Select not working, only giving last clicked value - reactjs

Question

I implemented a multiple select dropdown from react-bootstrap documentation.
It does not let me do multiple select and only gets the last clicked option. I have state variable set to array. What else am I missing? App is created with create-react-app.
I have state set to array inside the class constructor. Binding of event handler also done in the constructor.
Next, I'm showing my event handler followed by form group with onChange and value set to state. (note I have a drop-down above this which is working fine.)
I then pass this value to a few classes before it's parsed to JSON. The last pastes are those classes. I have removed other parameters so easier to read, any ideas, feel free to ask for more info.
this.state = {
codeCoverage: [],
}
this.handleCodeCoverageChange = this.handleCodeCoverageChange.bind(this);
//Event handlers below
handleCodeCoverageChange(event){
this.setState({
codeCoverage: event.target.value
})
}
<Form.Group>
<Form.Label>Please choose your desired code coverage software(s)</Form.Label>
<Form.Control as="select" value={this.state.codeCoverage} onChange={this.handleCodeCoverageChange} multiple>
<option value="">--Please choose an option--</option>
<option value="cobertura">Cobertura</option>
<option value="sonarcube">Sonarcube</option>
</Form.Control>
</Form.Group>
var configurator = new Configurator(this.state.codeCoverage)
class Configurator
{
constructor(
code_coverage)
{
this.pipeline = new Pipeline(code_coverage)
}
}
class Pipeline
{
constructor(code_coverage)
{
this.analysisAndSecurity = new AnalysisAndSecurity(code_coverage)
}
class AnalysisAndSecurity{
parameter
constructor(code_coverage)
{
this.code_coverage = code_coverage
}
}

Answer 1

In your handleChange function you assign state.codeCoverage the value of the selected element instead of adding it to the array of selected element. This is why when you select another element it deletes the old value. I would recommend logging e.target.value and this.state.codeCoverage to better understand. As for the solution:
Since you are using multiple select it expects an array as value instead of a single value. So you need to change two things in your handleChange method.
First you need to add your element to existing values and not replace them.
You need to handle when a selected element is clicked again and needs to become unselected.
You can do both these tasks as shown below:
handleChange = e => {
const { codeCoverage } = this.state;
// Find the value selected the codeCoverage array
const index = codeCoverage.indexOf(e.target.value);
// If the value is not found then add it to the array
if (index === -1) codeCoverage.push(e.target.value);
// If value found then remove the value to unselect
else codeCoverage.splice(index, 1);
// Set the state so that the component reloads with the new value
this.setState({ codeCoverage: [...codeCoverage] });
};