test.js

const classnames = require('classnames');

const props = {
    checked: true,
    color: 'red',
    disabled: true,
    focused: false,
    hovered: true,
    size: 'xl',
    type: null,
    width: null,
    className: 'MyRadio',
};

const N = 10000;

let r;
console.time('a');
for (let i = 0; i < N; i++) {
    const { checked, color, disabled, focused, hovered, size, type, width, className } = props;
    r = classnames(
        'Radio',
        {
            Radio_checked: checked,
            [`Radio_color_${ color }`]: color,
            Radio_disabled: disabled,
            Radio_focused: focused,
            Radio_hovered: hovered,
            [`Radio_size_${ size }`]: size,
            [`Radio_type_${ type }`]: type,
            [`Radio_width_${ width }`]: width,
        },
        className
    );
}
console.timeEnd('a');
console.log(r);

console.time('b');
for (let i = 0; i < N; i++) {
    let r = 'Radio';
    if (props.checked) {
        r += ' Radio_checked';
    }
    if (props.color) {
        r += ' Radio_color_' + props.color;
    }
    if (props.disabled) {
        r += ' Radio_disabled';
    }
    if (props.focused) {
        r += ' Radio_focused';
    }
    if (props.hovered) {
        r += ' Radio_hovered';
    }
    if (props.size) {
        r += ' Radio_size_' + props.size;
    }
    if (props.type) {
        r += ' Radio_type_' + props.type;
    }
    if (props.width) {
        r += ' Radio_width_' + props.width;
    }
    if (props.className) {
        r += ' ' + props.className;
    }
}
console.timeEnd('b');
console.log(r);

node test.js
a: 60.297ms
Radio Radio_checked Radio_color_red Radio_disabled Radio_hovered Radio_size_xl MyRadio
b: 4.178ms
Radio Radio_checked Radio_color_red Radio_disabled Radio_hovered Radio_size_xl MyRadio