A workaround for react-select 1.0.0 to implement allowCreate functionality

react-select-allowCreate.js

let isSelected = (values, selectedValue) => {
    if (!values || values.length < 1) {
        return false;
    }

    for (let { value } of values) {
        if (selectedValue === value) {
            return true;
        }
    }

    return false;
}

let filterOptions = (options, filter, currentValues) => {
    let filteredOptions = options.reduce((memo, option) => {
        // Optgroup support
        if (!('value' in option)) {
            memo.push(option);
        }

        // If a filter is present
        else if (filter && filter.length >= 1) {
            let valueNormalized = option.value.toLowerCase().trim();
            let filterNormalized = filter.toLowerCase().trim();

            if (valueNormalized.indexOf(filterNormalized) > -1) {
                memo.push(option);
            }
        }

        // Show everything available that's not already selected if no filter is used
        else if (!isSelected(currentValues, option.value)) {
            memo.push(option);
        }

        return memo;
    },
    []);

    // Only display `Add ${filter}` if no other options are available
    if (filteredOptions.length < 1 && filter) {
        filteredOptions.push({
            label: `Add ${filter}`,
            value: filter,
            create: true
        });
    }

    return filteredOptions;
}